I. CLASSIFICATION

A. Work of successive Systematists

Since the time when lichens were first recognized as a separate class—as members of the genus Lichen by Tournefort[1016] or as “Musco-fungi” by Morison[1017],—many schemes of classification have been outlined, and the history of the science of lichenology, as we have seen, is a record of attempts to understand their puzzling structure, and to express that understanding by relating them to each other and to allied classes of plants. The great diversity of opinion in regard to their affinities is directly due to their composite nature.

a. Dillenius and Linnaeus. The first systematists were chiefly impressed by their likeness to mosses, hepatics or algae. Dillenius[1018] in the Historia Muscorum grouped them under the moss genera:—IV. Usnea, V. Coralloides and VI. Lichenoides. Linnaeus[1019] classified them among algae under the general name Lichen, dividing them into eight orders based on thalline characters in all but one instance, the second order being distinguished from the first by bearing scutellae. The British botanists of the latter part of the eighteenth century—Hudson, Lightfoot and others—were content to follow Linnaeus and in general adopted his arrangement.

b. Acharius. Early in the nineteenth century Acharius, the Swedish Lichenologist, worked a revolution in the classification of lichens. He gave first place to the form of the thallus, but he also noted the fundamental differences in fruit-formation: his new system appeared in the Methodus Lichenum[1020] with an introduction explaining the terms he had introduced, many of them in use to this day.

Diagnoses of twenty-three genera are given with their included species. The work was further extended and emended in Lichenographia Universalis[1021] and in the Synopsis Lichenum[1022]. In his final arrangement the family “Lichenes” is divided into four classes, three of which are characterized solely by apothecial characters; the fourth class has no apothecia. They are as follows:

The orders are thus based on the form of the fruit; the genera in the Synopsis number 41. Large genera such as Lecanora with 132 species are divided into sections, many of which have in turn been established as genera, by S. F. Gray in 1821, and later by other systematists.

The Synopsis was the text-book adopted by succeeding botanists for some 40 years with slight alterations in the arrangement of classes, genera, etc.

Wallroth[1023] and Meyer[1024] followed with their studies on the lichen thallus, and Wallroth’s division into “Homoiomerous” and “Heteromerous” was accepted as a useful guide in the maze of forms, representing as it did a great natural distinction.

c. Schaerer. This valiant lichenologist worked continuously during the first half of the nineteenth century, but with very partial use of the microscope. His last publication in 1850, an Enumeration of Swiss Lichens, was the final declaration of the older school that relied on field characters. His classification is as follows:

An “Appendix” contains descriptions of Crustacei and Fruticulosi, all sterile forms, except Coniocarpon and Arthonia, which seem out of place, and finally a “Corollarium” of gelatinous lichens all classified under one genus Collema.

d. Massalongo and Koerber. As a result of their microscopic studies, these two workers proposed many changes based on fruit and spore characters, and Koerber in the Systema Lichenum Germaniae (1855) gave expression to these views in his classification. He also made use of Wallroth’s distinctions of “homoiomerous” and “heteromerous,” thus dividing lichens at the outset into those mostly with blue-green and those with bright-green gonidia.

The following is the main outline of Koerber’s classification:

With the exception of Order V all are subdivided into two sections, “gymnocarpi” with open fruits and “angiocarpi” with closed fruits, a distinction that had long been recognized both in lichens and in fungi.

e. Nylander. The above writers had been concerned with the interrelationships of lichens; Nylander, who was now coming forward as a lichenologist of note, gave a new turn to the study by dwelling on their relation to other classes of plants. Without for a moment conceding that they were either algal or fungal, he yet insisted on their remarkable affinity to algae on the one hand, and to fungi on the other, and he sought to make evident this double connection by his very ingenious scheme of classification[1025]. He began with what we may call “algal lichens,” those associated with blue-green gonidia in the family “Collemacei”; he continued the series to the most highly evolved foliose forms and then wound up with those that are most akin to fungi, that is, those with least apparent thalline formation—according to him—the “Pyrenocarpei.”

In his scheme, which is the one followed by Leighton and Crombie, the “family” represents the highest division; series, tribe, genus and species come next in order. We have thus:

This last family, which includes the great bulk of lichens, is divided into the following series: I. Epiconiodei; II. Cladoniodei; III. Ramalodei; IV. Phyllodei; V. Placodei; VI. Pyrenodei. It is an ascending series up to the Phyllodei, or foliaceous lichens, which he considers higher in development than the fruticose or filamentous Ramalodei. The Placodei include four tribes on a descending scale, the Lecanorei, Lecidinei, Xylographidei and Graphidei. The classification is almost wholly based on thalline form, except for the Pyrenodei in which are represented genera with closed fruits, there being one tribe only, the Pyrenocarpei.

Nylander claims however to have had regard equally to the reproductive system and was the first to give importance to the spermogonia. The classification is coherent and easy to follow, though, like all classifications based on imperfect knowledge, it is not a little artificial; also while magnifying the significance of spermogonia and spermatia, he overlooked the much more important characters of the ascospores.

f. Müller(-Argau). In preparing his lists of Genevan lichens (1862), Müller realized that Nylander’s series was unnatural, and he found as he studied more deeply that lichens must be ranged in parallel or convergent but detached groups. He recognized three main groups:

He suggested that, in relation to other plants, Eulichens approach Pezizae, Hysteriaceae and Sphaeriaceae; Epiconiaceae have affinity with Lycoperdaceae, while Collemaceae are allied to the algal family Nostocaceae. These three groups of Eulichens, he held, advanced on somewhat parallel lines, but reached a very varied development, the Discocarpeae attaining the highest stage of thalline form. Müller accepted as characters of generic importance the form and structure of the fruiting body, the presence or absence of paraphyses, and the septation, colour, etc. of the spores.

A few years later (1867) the composite nature of the lichen thallus was announced by Schwendener, and, after some time, was acknowledged by most botanists to be in accordance with the facts of nature. Any system of classification, therefore, that claims to be a natural one, must, while following as far as possible the line of plant development, take into account the double origin of lichens both from algae and fungi, the essential unity and coherence of the class being however proved by the recurring similarity between the thalline types of the different phyla. As Müller had surmised: “they are a series of parallel detached though convergent groups.”

g. Reinke. The arrangement of Ascolichens on these lines was first seriously studied by Reinke[1026], and his conclusions, which are embodied[1027] in the Lichens of Schleswig-Holstein, have been largely accepted by succeeding workers. He recognizes three great subclasses: 1. Coniocarpi; 2. Discocarpi; 3. Pyrenocarpi.

The Coniocarpi are a group apart, but as their fruit is at first entirely closed—at least in some of the genera—the more natural position for them is between Discocarpi and Pyrenocarpi. It is in the arrangement of the Discocarpi that variation occurs. Reinke’s arrangement of orders and families in that sub-class is as follows:

Subclass 2. Discocarpi.

The orders represent generally the principal phyla or groups, the families subordinate parallel phyla within the orders. The first three orders are stages of advance as regards fruit development; the Cyanophili are a group apart.

Wainio[1028] rendered great service to Phylogeny in his elaborate work on Cladoniaceae, the most complicated of all the lichen phyla. He also drew up a scheme of arrangement in his work on Brazil Lichens[1029]. There is in it some divergence from Reinke’s arrangement, as he tends to give more importance to the thallus than to fruit characters as a guide. He places, for instance, Gyrophorei beside Parmelei and at a long distance from his Lecidei. The Cyanophili group of families he has interpolated between Buelliae (Physciaceae) and Lecideae. Many workers approve of Wainio’s classification but it presents some difficult problems.

h. Zahlbruckner. The systematist of greatest weight in recent times is A. Zahlbruckner, who is responsible for the systematic account of lichens in Engler and Prantl’s Natürlichen Pflanzenfamilien. It is difficult to express the very great service he has rendered to Lichenology, in that and other world-wide studies of lichens. The sketch of lichen phylogeny as given in the present volume owes a great deal to the sound and clear guidance of his work, though his conclusions may not always have been accepted. The classification in the Pflanzenfamilien is the one now generally followed.

The class Lichenes is divided by Zahlbruckner[1030] into two subclasses, I. Ascolichens and II. Hymenolichens. He gives a third class, Gasterolichens[1031], but as it was founded on error[1032], it need not concern us here. The Ascolichens are by far the more important. These are subdivided into:

These are again broken up into families, and in the arrangement and sequence of the families Zahlbruckner indicates his view of development and relationship. They occur in the following order:

Series 1. PYRENOCARPEAE
Algal cells Protococcaceae or Palmella.
I.MORIOLACEAE.}Thallus crustaceous, perithecia solitary.
II.EPIGLOEACEAE.}
III.VERRUCARIACEAE.}
IV.DERMATOCARPACEAE.Thallus squamulose or foliose.
V.PYRENOTHAMNIACEAE.Thallus fruticose.
Algal cells Prasiola.
VI.MASTOIDIACEAE.
Algal cells Trentepohlia.
VII.PYRENULACEAE.}Thallus crustaceous, perithecia occurring singly.
VIII.PARATHELIACEAE.}
IX.TRYPETHELIACEAE.}Thallus crustaceous, perithecia united (stromatoid).
X.ASTROTHELIACEAE.}
XI.MYCOPORACEAE.Thallus crustaceous, perithecia in compact groups with a common outer wall.
XII.PHYLLOPYRENIACEAE.Thallus minutely foliose.
Algal cells Phyllactidium or Mycoidea.
XIII.STRIGULACEAE.Tropical leaf-lichens.
Algal cells Nostoc or Scytonema.
XIV.PYRENIDIACEAE.Thallus minutely squamulose or fruticose.
Series 2. GYMNOCARPEAE
Subseries 1. CONIOCARPINEAE

This is a well-defined group, peculiar in the disappearance of the asci at an early stage so that the spores lie like a powder in the globose partly closed fruits. Algal cells, bright-green; Protococcaceae. There are only three families:

XV.CALICIACEAE.Thallus crustaceous, apothecia stalked.
XVI.CYPHELIACEAE.Thallus crustaceous, apothecia sessile.
XVII.SPHAEROPHORACEAE.Thallus foliose or fruticose, apothecia sessile.
Subseries 2. GRAPHIDINEAE

This subseries comes next in the form of fruit development; generally the apothecia are elongate, with a narrow slit-like opening, so that a transverse section shows almost a perithecial outline. Algal cells are mostly Trentepohlia.

XVIII.ARTHONIACEAE.Thallus crustaceous, apothecia oval or linear, flat.
XIX.GRAPHIDACEAE.Thallus crustaceous, apothecia linear, raised.
XX.CHIODECTONACEAE.Thallus crustaceous, apothecia generally immersed in a stroma.
XXI.DIRINACEAE.Thallus crustaceous, corticate above, apothecia round.
XXII.ROCCELLACEAE.Thallus fruticose, apothecia round or elongate.
Subseries 3. CYCLOCARPINEAE

A large and very varied group! In most of the families the algal cells are bright-green (Chlorophyceae), in some they are blue-green (Cyanophyceae), these latter corresponding to Reinke’s order Cyanophili. The apothecia, as the name implies, are round and open; the “Cyanophili” have been placed by Zahlbruckner after those families in which the apothecium has no thalline margin. They form a phylum distinct from those that precede and those that follow.

The first family of the Cyclocarpineae, the Lecanactidaceae, is often placed under Graphidineae; in any case it forms a link between the two subseries.

1. Lecideine group (apothecia without a thalline margin).

XXIII.LECANACTIDACEAE.Thallus crustaceous. Algal cells Trentepohlia. Apothecium with carbonaceous hypothecium or parathecium.
XXIV.PILOCARPACEAE.Thallus crustaceous. Algal cells Protococcaceae. Apothecia with a dense rather dark hypothecium.
XXV.CHRYSOTHRICACEAE.Thallus felted, loose in texture. Algal cells Palmella, Protococcaceae or Trentepohlia. Apothecia with or without a thalline margin. The affinity of the “Family” seems to be with Pilocarpaceae.
XXVI.THELOTREMACEAE.}Thallus crustaceous. Algal cells in the first Trentepohlia; in the second Protococcaceae. In both there are prominent double margins round the apothecium.
XXVII.DIPLOSCHISTACEAE.}
XXVIII.ECTOLECHIACEAE.Thallus very primitive in type. Algal cells Protococcaceae. Apothecia with or without a thalline margin. Nearly related to Chrysothricaceae.
XXIX.GYALECTACEAE.Thallus crustaceous. Algal cells Trentepohlia, Phyllactidium or rarely Scytonema. Apothecia biatorine, i.e. of soft consistency and without gonidia.
XXX.COENOGONIACEAE.Thallus confusedly filamentous (byssoid). Algal cells Trentepohlia or Cladophora. Apothecia biatorine.
XXXI.LECIDEACEAE.Thallus crustaceous or squamulose. Algal cells Protococcaceae. Apothecia biatorine (soft), or lecideine (carbonaceous).
XXXII.PHYLLOPSORACEAE.Thallus squamulose or foliose. Algal cells Protococcaceae. Apothecia biatorine or lecideine.
XXXIII.CLADONIACEAE.Thallus twofold. Algal cells Protococcaceae. Apothecia biatorine or lecideine.
XXXIV.GYROPHORACEAE.Thallus foliose. Algal cells Protococcaceae. Apothecia lecideine.
XXXV.ACAROSPORACEAE.Thallus primitive crustaceous, squamulose or foliose. Algal cells Protococcaceae. Apothecia with or without a thalline margin; very various, but always with many-spored asci.

2. Cyanophili group.

In this group the classification depends almost entirely on the nature of the algal constituents. The apothecia are in most genera provided with a thalline margin.

a. More or less gelatinous when moist.

XXXVI.EPHEBACEAE.Algal cells Scytonema or Stigonema. Thallus minutely fruticose or filamentous.
XXXVII.PYRENOPSIDACEAE.Algal cells Gloeocapsa (Gloeocapsa, Xanthocapsa or Chroococcus). Thallus crustaceous, minutely foliose or fruticose.
XXXVIII.LICHINACEAE.Algal cells Rivularia. Thallus crustaceous, squamulose or minutely fruticose.
XXXIX.COLLEMACEAE.Algal cells Nostoc. Thallus crustaceous, minutely fruticose, or squamulose to foliose.
XL.HEPPIACEAE.Algal cells Scytonema. Thallus generally squamulose and formed of plectenchyma.

b. Not gelatinous when moist.

XLI.PANNARIACEAE.Algal cells Nostoc, Scytonema or rarely bright-green, Protococcaceae. Thallus crustaceous, squamulose or foliose.
XLII.STICTACEAE.Algal cells Nostoc or Protococcaceae. Thallus foliose, and very highly developed, corticate on both surfaces.
XLIII.PELTIGERACEAE.Algal cells Nostoc or Protococcaceae. Thallus foliose, corticate above.

3. Lecanorine group (apothecia with a thalline margin).

The remaining families have all bright-green gonidia and nearly always apothecia with a thalline margin. The group includes several distinct phyla:

XLIV.PERTUSARIACEAE.Thallus crustaceous. Apothecia, one or several immersed in thalline tubercles; spores mostly very large.
XLV.LECANORACEAE.Thallus crustaceous or squamulose. Apothecia mostly superficial.
XLVI.PARMELIACEAE.Thallus foliose, rarely almost fruticose or filamentous. Apothecia scattered over the surface or marginal, sessile.
XLVII.USNEACEAE.Thallus fruticose or filamentous. Apothecia sessile or shortly stalked.
XLVIII.CALOPLACACEAE.Thallus crustaceous, squamulose or minutely fruticose. Apothecia with polarilocular colourless spores.
XLIX.TELOSCHISTACEAE.Thallus foliose or fruticose. Apothecia with polarilocular colourless spores.
L.BUELLIACEAE.Thallus crustaceous or squamulose. Apothecia (lecideine or lecanorine) with two-celled, thick-walled brown spores (polarilocular in part).
LI.PHYSCIACEAE.Thallus foliose, rarely partly fruticose. Apothecia with two-celled thick-walled brown spores (polarilocular in part).
Subclass 2. Hymenolichens.

There are only three closely related genera of Hymenolichens, Cora, Corella and Dictyonema with Chroococcus or Scytonema algae.

There is reason to dissent from the arrangement in one or two instances which will be pointed out in the following examination of families and genera.

B. Families and Genera of Ascolichens

The necessity for a well-reasoned and well-arranged system of classification is self-evident: without a working knowledge of the plants that are the subject of study no progress can be made. The recognition of plants as isolated individuals is not sufficient, it must be possible to place them in relation to others; hence the importance of a natural system. In identifying species artificial aids, such as habitat and substratum, are also often of great value, and a good working system should take account of all characteristics.

Lichen development is the result of two organisms mutually affecting each other, but as the fungus provides the reproductive system, it is the dominant partner: the main lines of classification are necessarily determined by fruit characters. The algae occupy a subsidiary position, but they also are of importance in shaping the form and structure of the thallus. The different phyla are often determined by the presence of some particular alga; it is in the delimitation of families that the algal influence is of most effect.

Zahlbruckner’s system gives due weight to the inheritance from both fungus and alga with, however, the fungus as the chief factor in development, and as his work is certain to be generally followed by modern lichenologists, it is the one of most immediate interest. His scheme has been accepted in the following more detailed account of families and genera, and for the benefit of home workers those that have not so far been recorded from the British Isles have been marked with an asterisk.

It cannot be affirmed that nomenclature is as yet firmly established in lichenology. Both on historical grounds and on those of convenience, the subject is one of extreme importance, and interest in it is one of the main avenues by which we secure continuity with the past, and by which we are able to realize not only the difficulty, but the romance of pioneer work. Besides, there can be no exchange of opinion between students nor assured knowledge of plants, until the names given to them are beyond dispute. According to the ruling of the Brussels Botanical Congress in 1910, Linnaeus’s[1033] list of lichens in the Species Plantarum has been selected as the basis of nomenclature, but since his day many new families, genera and species have been described and often insufficiently delimited. It is not easy to decide between priority, which appeals to the historical sense, and recent use which is the plea of convenience. Here also it seems there can be no rigid decision; the one aim should be to arrive at a conclusion satisfactory to all, and accepted by all.

In the following necessarily brief account of families and genera, the “spermogonia” or “pycnidia” have in most cases been left out of account, as in many instances they vary within the family and occasionally even within the genus. Their taxonomic value is not without importance, but, in the general systematic arrangement, they are only subsidiary characters. An account of them has already been given, and for more detailed statements the student is referred to purely systematic works.

There are two main types of spore production in the “pycnidia” which have been shortly described by Steiner[1034] as “exobasidial” and “endobasidial.” In the former the sporophores are simple or branched filaments, at the apices of which a short process grows out and buds off a pycnidiospore; in the latter the spores are budded directly from cells lining the walls or filling the cavity of the pycnidium. The exobasidial type is more simply rendered in the following pages by “acrogenous,” the endobasidial by “pleurogenous” spore production. In many cases the “spermogonia” or “pycnidia” are still imperfectly known. In designating the gonidial algae, the more comprehensive Protococcaceae has been substituted for Protococcus, as in many cases the alga is probably not Protococcus as now understood, but some other genus of the family[1035].

Subclass I. ASCOLICHENS

Series I. PYRENOCARPINEAE

It is on mycological grounds that Pyrenocarpineae are placed at the base of lichen classification. There is no evidence that the series was first in time.

I. Moriolaceae

This family was described by Norman[1036] in 1872 from specimens collected by himself in Norway or in the Tyrol, on soil or more frequently on trees. There seems to have been no further record, and Zahlbruckner, while accepting the family, suggests that an examination or revision may be necessary.

The thallus is crustaceous. The algal cells, Protococcaceae, occur either in groups (sometimes stalked) surrounded by a plectenchymatous wall and called by Norman “goniocysts,” or they form nests in the thallus termed “nuclei” which are surrounded by a double wall of plectenchyma, colourless in the interior and brown outside. Norman invented the term “Allelositismus,” which may be rendered “mutualism,” to indicate this peculiar form of thallus. The species of Spheconisca are fairly numerous on poplars, willows and conifers:

Algae in “goniocysts”1.*Moriola Norm.[1037]
Algae in double-walled “nuclei”2.*Spheconisca Norm.
II. Epigloeaceae

The family consists of but one genus and one species, Epigloea bactrospora, and, according to Zahlbruckner, further examination is necessary to make certain as to the lichenoid nature of the plant.

Zukal[1038] found the perithecia scattered over the leaves of mosses, and he alleges that hyphae connected with the perithecium were closely associated with the alga, Palmella botryoides, and were causing it no harm. Along with the perithecia he also found minute pycnidia. The “thallus” is of a gelatinous nature and homoiomerous in structure; the perithecia are soft and clear-coloured with many-spored asci and colourless one-septate spores.

The small globose pycnidia contain simple sporophores and acrogenous straight or slightly bent rod-like spores.

Asci many-spored; spores one-septate1.*Epigloea Zukal.

III. Verrucariaceae

In all the genera of this family the thallus is crustaceous, and, with very few exceptions, the species are saxicolous or terricolous. The thallus is variable within the crustaceous limits, and may be superficial and very conspicuous, almost imperceptible, or wholly immersed in the substratum. The algal cells are Protococcaceae, and in two of the genera the green cells penetrate the hymenium and grow in rows alongside of the asci. The perithecia are small roundish structures scattered over the thallus, the base immersed, but the upper portion generally projecting. An outer dark-coloured wall surrounds the whole perithecium (entire) or only the upper exposed portion (dimidiate); it opens above by a pore or ostiole more or less prominent.

In some of the genera the paraphyses become dissolved at an early stage, and somewhat similar filaments near the ostiole, termed periphyses, aid in the expulsion of the spores. The spores vary in septation, colour and size, and these variations have served to delimit the genera which have been formed from the original very large genus Verrucaria. The ascus may be 1-, 2-, 4- or 8-spored. In only one genus is it many-spored (Trimmatothele).

The genera are as follows:

Perithecia with simple ostioles.
Paraphyses disappearing early, or wanting.
Spores simple, ellipsoid1.Verrucaria Web.
Spores simple, elongate vermiform2.Sarcopyrenia Nyl.
Spores simple, numerous in the ascus3.*Trimmatothele Norm.
Spores 1-3-septate4.Thelidium Massal.
Spores muriform (with transverse and longitudinal divisions).
Without hymenial gonidia5.Polyblastia Massal.
With hymenial gonidia6.Staurothele Norm.
Paraphyses present.
Spores simple.
Without hymenial gonidia7.Thrombium Wallr.
With hymenial gonidia8.*Thelenidia Nyl.
Spores 3-septate, broadly ellipsoid9.*Geisleria Nitschke.
Spores acicular, many-septate10.Gongylia Koerb.
Spores muriform11.Microglaena Lönnr.
Perithecia with a wide ring round the ostiole.
Spores muriform; paraphyses unbranched12.*Aspidothelium Wain.
Spores elongate, many-septate; paraphyses branched13.*Aspidopyrenium Wain.
IV. Dermatocarpaceae

In this family there is a much more advanced thalline development—generally squamulose or with some degree of foliose structure, though in the genus Endocarpon, some of the species are little more than crustaceous. The gonidia are bright-green Protococcaceae (according to Chodat, Coccobotrys in Dermatocarpon). In Endocarpon they appear in the hymenium.

The least developed in structure is Normandina: the thallus of the single species consists of delicate shell-like squamules which are non-corticate above and below. In the other genera there is a cortex of plectenchyma.

The perithecia are almost wholly immersed, and open above by a straight ostiole. The fructification of Dacampia is considered by some lichenologists to be only a parasite on the white thickish squamulose thallus with which it is associated.

Hymenial gonidia present.
Spores muriform1.Endocarpon Hedw.
Hymenial gonidia absent.
Thallus non-corticate2.Normandina Wain.
Thallus corticate.
Spores simple, colourless3.Dermatocarpon Eschw.
Spores simple, brown4.*Anapyrenium Müll.-Arg.
Spores elongate-septate, colourless5.*Placidiopsis Beltr.
Spores elongate-septate, brown6.*Heterocarpon Müll.-Arg.
Spores muriform, colourless7.*Psoroglaena Müll.-Arg.
Spores muriform, brown8.Dacampia Massal.
V. Pyrenothamniaceae

Thallus more or less fruticose and corticate on both surfaces. Algal cells Protococcaceae.

Only two genera are included in this family: Nylanderiella with one species from New Zealand, with a small laciniate thallus up to 15 mm. in height, partly upright, partly decumbent, and attached to the substratum by basal rhizinae; the other small genus, Pyrenothamnia, belongs to N. America; the thallus has a short rounded stalk which expands above to an irregular frond. The perithecia are immersed in the fronds.

Spores colourless, 1-septate1.*Nylanderiella Hue[1039].
Spores brown, muriform2.*Pyrenothamnia Tuckerm.
VI. Mastoideaceae

A family containing one genus and one species, with a wide distribution, having been found in Siberia, on the Antarctic continent (Graham’s Land), as also in Tierra del Fuego, South Georgia, South Shetland Islands and Kerguelen. The thallus is foliose, of small thin lobes, and without rhizinae. Algal cells Prasiola[1040]. The perithecia are globose and partly project from the thallus; the asci are 8-spored; the paraphyses are mucilaginous and partly dissolving.

Spores elongate-fusiform, simple, colourless1.*Mastoidea Hook. and Harv.

VII. Pyrenulaceae

This family of crustaceous lichens differs from Verrucariaceae chiefly in the gonidium which is a species of Trentepohlia. Genera and species are largely corticolous and the thallus is inconspicuous, often developing within the substratum. The perithecia, like those of Verrucariae, are immersed or partly emergent and have an entire or dimidiate outer wall. They are scattered over the thallus except in Anthracothecium where they are often coalescent. This genus is tropical or subtropical except for one species which inhabits S.W. Ireland.

Paraphyses are variable, and in some species tend to disappear, but do not dissolve in mucilage. The spores are generally colourless, only in one monotypic genus, Coccotrema, are they simple. The cells into which the spore is divided differ in form according to the genus.

Paraphyses branched and entangled or wanting.
Perithecia opening above by stellate lobes1.*Asteroporum Müll.-Arg.
Perithecia opening by a pore.
Spores variously septate.
Spore cells cylindrical or cuboid.
Spores colourless, elongate or ovate 1-5-septate2.Arthopyrenia Massal.
Spores colourless, filiform 1-multi-septate3.Leptorhaphis Koerb.
Spores colourless, muriform4.Polyblastropsis A. Zahlbr.
Spores brown, ovoid or elongate 2-5-septate5.Microthelia Koerb.
Spore cells globose or lentiform, 3-multi-septate6.*Pseudopyrenula Müll.-Arg.
Paraphyses unbranched free.
Spore cells cylindrical or cuboid.
Perithecia beset with hairs7.*Stereochlamys Müll.-Arg.
Perithecia naked.
Asci disappearing; spores elongate multi-septate, colourless8.*Belonia Koerb.
Asci persistent.
Spores simple, ellipsoid, colourless9.*Coccotrema Müll.-Arg.
Spores elongate, 1-multi-septate, colourless10.Porina Müll.-Arg.
Spores elongate, 1-multi-septate, brown11.Blastodesmia Massal.
Spores muriform, colourless12.*Clathroporina Müll.-Arg.
Spores elongate, 2-3-septate, colourless13.Thelopsis Nyl.
Spore cells globose or lentiform.
Spores elongate, 1-5-septate, brown14.Pyrenula Massal.
Spores muriform, brown15.Anthracothecium Massal.
VIII. Paratheliaceae

This family is peculiar in that the perithecia open by a somewhat elongate ostiole that slants at an oblique angle. The algal cells are Trentepohlia. Genera and species are endemic in tropical or subtropical regions of the Western hemisphere, though a species of Pleurotrema has been found in subantarctic America. They are corticolous and the thallus is either superficial or embedded. The genera are arranged according to spore characters:

Spores elongate, 2- or more-septate.
Spore cells cylindrical, colourless1.*Pleurotrema Müll.-Arg.
Spore cells globose-lentiform.
Spores colourless2.*Plagiotrema Müll.-Arg.
Spores brown3.*Parathelium Müll.-Arg.
Spores muriform.
Spores colourless4.*Campylothelium Müll.-Arg.
Spores brown5.*Pleurothelium Müll.-Arg.
IX. Trypetheliaceae

This and the following two families are distinguished by the pseudostroma or compound fruit, a character rare among lichens, though the true stroma is frequent in Pyrenomycetes in such genera as Dothidea, Valsa, etc. The genera are crustaceous and corticolous and occur with few exceptions in tropical or subtropical regions, mostly in the Western Hemisphere. Several grow on officinal bark (Cinchona, etc.). Algal cells are Trentepohlia. As in many tropical lichens, the spores are large. The genera are based chiefly on spore characters, on septation, and on the form of the spore cells:

Spore cells cylindrical or cuboid.
Spores colourless, elongate, multi-septate1.*Tomasiella Müll.-Arg.
Spores colourless, muriform2.*Laurera Rehb.
Spores brown, muriform3.*Bottaria Massal.
Spore cells globose-lentiform.
Spores colourless, elongate, multi-septate4.*Trypethelium Spreng.
Spores brown, elongate, multi-septate5.Melanotheca Müll.-Arg.
X. Astrotheliaceae

The perithecia are either upright or inclined, and occur usually in radiate groups. They are free or united in a stroma, and the elongate ostioles open separately or coalesce in a common canal. The genera are all crustaceous, with Trentepohlia gonidia. They are tropical or subtropical, mostly in the Western Hemisphere; but species of Parmentaria and Astrothelium have been recorded also from Australia.

The spores are all many-celled and the form of their cells is a generic character:

Spores elongate, multi-septate.
Spore cells cylindrical1.*Lithothelium Müll.-Arg.
Spore cells globose-lentiform.
Spores colourless2.*Astrothelium Trev.
Spores brown3.*Pyrenastrum Eschw.
Spores muriform.
Spores colourless4.*Heufleria Trev.
Spores brown5.*Parmentaria Fée.

XI. Mycoporaceae

A small family with only two genera which are found in both Hemispheres; species of both occur in Great Britain. They are all corticolous. The perithecia are united into a partially chambered fruiting body surrounded by a common wall, but opening by separate ostioles. The thallus is thinly crustaceous, with Palmella gonidia in Mycoporum, and Trentepohlia in Mycoporellum. The spores are colourless or brown in both genera:

Spores muriform1.Mycoporum Flot.
Spores elongate, multi-septate2.Mycoporellum A. Zahlbr.
XII. Phyllopyreniaceae

Thallus foliose with both surfaces corticate and attached by rhizinae. Algal cells Trentepohlia. There is but one genus, Lepolichen, which has a laciniate somewhat upward growing thallus. Two species, both from South America, have been described, L. granulatus Müll.-Arg. and L. coccophora Hue. The latter has been recently examined by Hue[1041] who finds, on the thalli, cephalodia which are peculiar in containing bright-green gelatinous algae either Urococcus or Gloeocystis, one of the few instances known of chlorophyllaceous algae forming part of a cephalodium. Gloeocystis may be the only alga present in the cephalodium; Urococcus is always accompanied by Scytonema.

The perithecia are immersed in thalline tubercles:

Spores colourless, simple, ovoid or ovoid-elongate1.*Lepolichen Trevis.
XIII. Strigulaceae

A family of epiphyllous lichens inhabiting and disfiguring coriaceous evergreen leaves, or occasionally fern leaves in tropical or subtropical regions. The algae associated are Mycoidea and Phycopeltis (Phyllactidium). The only truly parasitic lichen, Strigula, belongs to this family: the alga precedes the lichen on the leaves and is gradually invaded by the hyphae of the lichen and altered in character. The small black perithecia are scattered over the surface. In Strigula the lichen retains the spreading rounded form of the alga. The other genera are more irregular.

Thallus orbicular in outline1.*Strigula Fries.
Thallus irregular.
Perithecia without hairs.
Spores colourless.
Spores elongate, multi-septate2.*Phylloporina Müll.-Arg.
Spores muriform3.*Phyllobathelium Müll.-Arg.
Spores brown.
Spores simple4.*Haplopyrenula Müll.-Arg.
Spores elongate, 1-3-septate5.*Microtheliopsis Müll.-Arg.
Perithecia beset with stiff hairs6.*Trichothelium Müll.-Arg.

XIV. Pyrenidiaceae

The only family of Pyrenocarpineae associated with blue-green algae. The genera of Pyrenidiaceae are all monotypic, only one is common and of wide distribution, Coriscium (Normandina Nyl.). Pyrenidium is the only member that has a fruticose thallus, and that is of minute dimensions. Eolichen Heppii, found and described by Zukal, is a doubtful lichen. “Lophothelium” Stirton is a case of parasitism of a fungus, Ticothecium, on the squamules of Stereocaulon condensatum.

Algal cells Scytonema or Stigonema.
Thallus crustaceous[1042]; spores simple, colourless1.*Rhabdopsora Müll.-Arg.
Thallus crustaceous; spores 1-septate, colourless2.*Eolichen Zuk.
Thallus crustaceous; spores muriform, brown3.*Pyrenothrix Riddle[1043].
Thallus squamulose; spores numerous, simple4.*Placothelium Müll.-Arg.
Algal cells Nostoc.
Thallus crustaceous; spores filiform, simple, colourless5.*Hassea A. Zahlbr.
Thallus fruticose; spores elongate, 3-septate, brown6. Pyrenidium Nyl.
Algal cells Microcystis (Polycoccus).
Thallus squamulose; fructification unknown7. Coriscium Wainio.
Series II. GYMNOCARPEAE

Subseries 1. Coniocarpineae

This small subseries is marked by the peculiar “mazaedium” type of fruit with its disappearing asci. It forms a connecting link between the families with perithecia and those with apothecia. The thallus is crustaceous or fruticose, often poorly developed and sometimes absent. The algal cells are Protococcaceae or rarely Trentepohlia.

XV. Caliceaceae

The thallus is thinly crustaceous, sometimes brightly coloured, sometimes absent, taking no part in the formation of the fruits; these have upright stalks with a small capitulum, and often look like minute nails. One genus, Sphinctrina, is parasitic on the thallus of other lichens, mostly Pertusariae.

Fruits with slender stalks.
Spores simple.
Spores colourless1.Coniocybe Ach.
Spores brown2.Chaenotheca Th. Fr.
Spores septate, brown.
Spores 1-septate3.Calicium De Not.
Spores 3-7-septate4.Stenocybe Nyl.
Fruits with short thick stalks.
Spores globose, brown (parasitic)5.Sphinctrina Fries.
Spores 1-septate, brown6.*Pyrgidium Nyl.

XVI. Cypheliaceae

Thallus crustaceous. Algal cells Protococcaceae or Trentepohlia. Apothecia sessile, more widely open than in the previous family; in some genera the thallus forms an outer apothecial margin. The genera Farriola from Norway and Tylophorella from New Granada are monotypic. The British genus Cyphelium has been known as Trachylia.

Thallus with Protococcaceae.
Spores colourless, simple1.*Farriola Norm.
Spores brown, 1-3-septate (rarely simple or muriform)2. Cyphelium Th. Fr.
Thallus with Trentepohlia.
Spores simple, many in the ascus3.*Tylophorella Wainio.
Spores 8 in the ascus.
Apothecia with a thalline margin4.*Tylophoron Nyl.
Apothecia without a thalline margin5.*Pyrgillus Nyl.
XVII. Sphaerophoraceae

The most highly evolved family of the subseries, as regards the thallus. Algal cells Protococcaceae. In Tholurna, a small lichen endemic in Scandinavia, there is a double thallus: one of horizontal much-divided squamules, the other swollen, upright, terminating in the capitulum. The fruit is lateral in Calycidium, a squamulose form from New Zealand, and in Pleurocybe from Madagascar, with stiff strap-shaped fronds. All the genera are monotypic except Sphaerophorus, of which genus ten species are recorded, some of them with a world-wide distribution. The spores are brown and simple or 1-septate.

Thallus squamulose and upright1.*Tholurna Norm.
Thallus wholly squamulose2.*Calycidium Stirton.
Thallus fruticose.
Fronds hollow in the centre3.*Pleurocybe Müll.-Arg.
Fronds not hollow.
Fruit without a thalline margin4.*Acroscyphus Lév.
Fruit inclosed in the tip of the fronds5.Sphaerophorus Pers.

Subseries 2. Graphidineae

In this subseries are included five families that differ rather widely from each other both in thallus and apothecia; the latter are more or less carbonaceous and mostly with a proper margin only. Families and genera are widely distributed, though most abundant in warm regions. Algal cells mostly Trentepohlia.

A comprehensive study of the apothecia of this series by Bioret[1044] gives some interesting results in regard to the paraphyses: in Arthonia they are irregular in direction and much-branched; in Opegrapha, the paraphyses are vertical and parallel with more regular branching; Stigmatidium (Enterographa) resembles Opegrapha in this respect as does also Platygrapha, a genus of Lecanactidaceae, while in Graphis the paraphyses are vertical, unbranched and free; Melaspilea paraphyses are somewhat similar to those of Graphis.

XVIII. Arthoniaceae

The thallus of Arthoniaceae is corticolous with few exceptions and is very inconspicuous, being largely embedded in the substratum. The apothecia (ardellae) are round, irregular or stellate, without any margin, the hymenium being protected by the dense branching of the paraphyses at the tips.

Arthonia is abundant everywhere. The species of the other genera belong mostly to tropical or subtropical countries. Arthoniopsis is similar to Arthonia in the character of the fruits, but the gonidium is a Phycopeltis, and it is only found on leaves. Synarthonia with peculiar stromatoid fructification is monotypic; it occurs in Costa Rica.

Thallus with Trentepohlia gonidia.
Apothecia scattered.
Spores elongate 1- or pluri-septate1.Arthonia Ach.
Spores muriform2.Arthothelium Massal.
Apothecia stromatoid.
Spores elongate, multi-septate3.*Synarthonia Müll.-Arg.
Thallus with Palmella gonidia.
Spores 1- or more-septate4.Allarthonia Nyl.
Spores muriform5.*Allarthothelium Wain.
Thallus with Phycopeltis gonidia.
Spores elongate 1- or more-septate6.*Arthoniopsis Müll.-Arg.
XIX. Graphidaceae

Thallus crustaceous, inconspicuous, partly immersed, mainly growing on bark but occasionally on dead wood or stone. Algal cells chiefly Trentepohlia, very rarely Palmella or Phycopeltis (epiphyllous). Apothecia (lirellae) carbonaceous more or less linear, opening by a narrow slit with a well-developed proper margin except in Gymnographa, a monotypic Australian genus. In two genera, the fruit is of a compound nature, several parallel discs occurring in one lirella: these are Ptychographa (on bark in Scotland) and Diplogramma (Australia), both are monotypic. They must not be confused with Graphis elegans and allied species in which the sterile carbonaceous margin is furrowed. Two tropical genera associated with Phycopeltis are epiphyllous.

Graphidaceae are among the oldest recorded lichens, attention having been drawn to them since early times by the resemblance of the lirellae on the bark of trees to hieroglyphic writing.

Thallus with Palmella gonidia.
Apothecia single.
Hypothecium dark-brown.
Spores simple1.Lithographa Nyl.
Hypothecium colourless or brownish.
Spores colourless.
Spores simple2.Xylographa Fries.
Spores elongate 3-8-septate3.*Aulaxina Fée.
Spores brown.
Spores 1-septate4.Encephalographa Massal.
Spores pluri-septate, then muriform5.*Xyloschistes Wain.
Apothecia compound.
Spores simple, colourless6.Ptychographa Nyl.
Spores pluri-septate, colourless7.*Diplogramma Müll.-Arg.
Thallus with Trentepohlia gonidia.
Spores elongate 1-multi-septate, the cells longer than wide.
Spores brown.
Spores 1-(rarely more)-septate8.Melaspilea Nyl.
Spores 3-septate (apothecia rudimentary)9.*Gymnographa Müll.-Arg.
Spores colourless.
Spores acicular, coiled (many in the ascus)10.*Spirographa A. Zahlbr.
Spores fusiform, straight11.Opegrapha Humb.
Spores muriform.
Spores elongate, central cells finally muriform12.*Dictyographa Müll.-Arg.
Spores elongate, septate, cells wider than long.
Paraphyses unbranched, filiform.
Spores multi-septate, colourless13.Graphis Adans.
Spores multi-septate, brown14.Phaeographis Müll.-Arg.
Spores muriform, colourless15.Graphina Müll.-Arg.
Spores muriform, brown16.Phaeographina Müll.-Arg.
Paraphyses clavate, warted at tips17.*Acanthothecium Wain.
Paraphyses branched, interwoven above18.*Helminthocarpon Fée.
Thallus with Phycopeltis gonidia (epiphyllous).
Spores elongate, 3-9-septate, colourless19.*Opegraphella Müll.-Arg.
Spores elongate, 1-septate, brown20.*Micrographa Müll.-Arg.
XX. Chiodectonaceae

Specially distinguished in this subseries by the grouping of the somewhat rudimentary apothecia in pseudostromata in which they are almost wholly immersed. In form they are roundish or linear; the spores are septate or muriform. The thallus is thinly crustaceous and continuous: in Glyphis, Sarcographa and Sarcographina there is an amorphous upper cortex, the other genera are non-corticate. Algal cells are Trentepohlia with the exception of two epiphyllous genera associated with Phycopeltis.

Genera and species are mostly tropical. Sclerophyton with five species is represented in Europe by a single British specimen, S. circumscriptum.

The form of the paraphyses is a distinguishing character of the genera.

Thallus with Trentepohlia gonidia.
Paraphyses free, unbranched.
Spore cells short or almost globose.
Spores elongate, multi-septate, colourless1.Glyphis Fée.
Spores elongate, multi-septate, brown2.*Sarcographa Fée.
Spores muriform, brown3.*Sarcographina Müll.-Arg.
Spore cells longer and cuboid.
Spores muriform, colourless4.*Enterodictyon Müll.-Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate, colourless5.Chiodecton Ach.
Spores elongate, multi-septate, brown6.Sclerophyton Eschw.
Spores muriform, colourless7.*Minksia Müll.-Arg.
Spores muriform, brown8.*Enterostigma Müll.-Arg.
Thallus with Phycopeltis gonidia (epiphyllous).
Paraphyses free.
Spores unequally 2-celled, colourless9.*Pycnographa Müll.-Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate, colourless10.*Mazosia Massal.
XXI. Dirinaceae

A small family, which is associated with and often included under Graphidaceae. The thallus is crustaceous and corticate on the upper surface, the cortex being formed of palisade hyphae. Algal cells Trentepohlia. Apothecia are rounded or with a tendency to elongation, and, in addition to a thin proper margin, possess a stout thalline margin; the hypothecium is thick and carbonaceous. There are two genera: Dirina with twelve species has a wide distribution; Dirinastrum is monotypic and occurs on maritime rocks in Australia. In both the spores are elongate-septate, differing only in colour:

Spores colourless1. Dirina Fr.
Spores brown2.*Dirinastrum Müll.-Arg.
XXII. Roccellaceae

The Roccellaceae differ from the preceding Dirinaceae chiefly in the fruticose thallus which is more or less characteristic of all the genera, though in Roccellographa it expands into foliose dimensions and in Roccellina is reduced to short podetia-like processes from a crustose base. The fronds—mostly long and strap-shaped—are protected in most of the genera by a cortex of compact palisade hyphae; in a few the outer hyphae are parallel with the long axis. The medulla is of parallel hyphae, either loose or compact. The algal cells are Trentepohlia.

The apothecia are lateral except in Roccellina where they occur at the tips of the short upright fronds, and only in Roccellaria is there no thalline margin. They are superficial in all of the genera except Roccellographa, in which they are immersed and almost closed, recalling the perithecia-like fruits of Chiodecton (sect. Enterographa). The spores are elongate, narrow, pluri-septate, and colourless or brownish, except in Darbishirella in which they are ovoid, 2-septate and brown.

The affinity of Dirinaceae and Roccellaceae with Graphidaceae was first indicated by Reinke[1045] and elaborated later by Darbishire[1046] in his monograph of Roccellaceae. The apothecia in some species of Dirina are ellipsoid rather than round; in several genera of Roccellaceae they are distinctly lirellate, and in Roccella itself some species have ellipsoid fruits. The fruticose thallus is predominant in Roccellaceae, but its evolution from the crustaceous type may be traced through Roccellina which is partly crustaceous and only imperfectly fruticose.

In most of the genera only one species is recorded. Roccella, represented by twelve species, is well known for its dyeing properties, and has a wide distribution. Like other Graphidineae they are mainly plants of warm regions, many of them exclusively maritime rock-dwellers.

The following synopsis of the genera is the one given by Darbishire in his monograph.

Cortex fastigate, of palisade hyphae.
Spores colourless.
Hypothecium black-carbonaceous.
Apothecia round.
Thallus fruticose1.Roccella DC.
Thallus crustaceous-fruticose2.*Roccellina Darbish.
Apothecia lirellate3.*Reinkella Darbish.
Hypothecium colourless.
Gonidia present under the hypothecium4.*Pentagenella Darbish.
Gonidia absent from hypothecium5.*Combea De Not.
Spores brown or brownish.
Medulla of parallel somewhat loose hyphae6.*Schizopelte Th. Fr.
Medulla solid, black7.*Simonyella Steiner.
Cortex fibrous, of parallel hyphae.
Apothecia round.
Hypothecium black-carbonaceous.
Apothecia with thalline margin8.*Dendrographa Darbish.
Apothecia with proper margin9.*Roccellaria Darbish.
Hypothecium colourless10.*Darbishirella A. Zahlbr.
Apothecia lirellate11.*Ingaderia Darbish.

Subseries 3. Cyclocarpineae

This last subseries includes the remaining twenty-nine families of Ascolichens. They are very varied both in the fungal and the algal symbionts. The fruit is more or less a discoid open apothecium. The gonidia belong to different genera of Myxophyceae and Chlorophyceae, but the most frequent are Protococcaceae. Families are based largely on thalline structure.

XXIII. Lecanactidaceae

By many systematists this family is included under Graphidineae on account of the fruit structure which in some of the forms is carbonaceous and almost lirellate, and also because the algal symbiont is Trentepohlia. The thallus is primitive, being thinly crustaceous and non-corticate; the apothecium has a black carbonaceous hypothecium in two of the genera, Lecanactis and Schismatomma (Platygrapha); in the third genus, Melampydium, it is colourless. The latter is monotypic, and the spores become muriform. In the other genera they are elongate and multi-septate.

Apothecia with prominent proper margin1. Lecanactis Eschw.
Apothecia with thin proper margin2.*Melampydium Müll.-Arg.
Apothecia with thalline margin3. Schismatomma Flot.
XXIV. Pilocarpaceae

A small family with but one genus, Pilocarpon. It is distinguished as one of the few epiphyllous genera of lichens associated with Protococcaceous gonidia and with a distribution extending far beyond the tropics. The best known species, P. leucoblepharum, encircles the base of pine-needles with a white felted crust, or inhabits coriaceous evergreen leaves. Another species lives on fern leaves. The fruit is a discoid apothecium with a dark carbonaceous hypothecium and proper margin, and with a second thalline margin. The paraphyses are branched and interwoven above.

Spores elongate, 3-septate, colourless1. Pilocarpon Wain.
XXV. Chrysotrichaceae

This family now, according to Hue[1047], includes two genera, Crocynia and Chrysothrix. In both there is a thallus of interlaced hyphae with Protococcaceous algae scattered through it or in groups. The structure is thus homoiomerous, and Hue has suggested for it a new series, “Intertextae.” The only British species, Crocynia lanuginosa, first placed by Nylander[1048] in Amphiloma and later transferred by him to Leproloma[1049], has a soft crustaceous lobate thallus, furfuraceous on the surface; no fructification has been found. A West Indian species, C. gossypina, has discoid apothecia with a thalline margin. There is only one species of Chrysothrix, Ch. nolitangere, which forms small clumps or tufts on the spines of Cactus in Chili. The structure is somewhat similar to that of Crocynia.

Spores colourless, simple1. Crocynia Nyl.
Spores colourless, 2-3-septate2.*Chrysothrix Mont.

XXVI. Thelotremaceae

A tropical or subtropical family of which the leading characteristic is the deeply sunk disc of the apothecium: it has a proper hyphal margin, and, round that, an overarching thalline margin. The apothecia occur singly, or they are united in a kind of pseudostroma: in Tremotylium several grow together, while in Polystroma each new apothecium develops as an outgrowth from the thalline margin of the one already formed, so that an upright, branching succession of fruits is built up. It is a very unusual type of lichen fructification, with one species, P. Ferdinandezii, found in Spain and in Guiana.

The thallus in all the genera is crustaceous with an amorphous (decomposed) cortex; or it is non-corticate. The algal cells are Trentepohlia except in Phyllophthalmaria, an epiphyllous genus associated with the alga Phycopeltis. In Polystroma the alga is unknown.

Only one genus is represented in the British Isles.

Apothecia growing singly.
Thallus with Trentepohlia gonidia.
Paraphyses numerous, unbranched, free.
Spores colourless.
Spores elongate, 2- or multi-septate1.*Ocellularia Spreng.
Spores muriform2.Thelotrema Ach.
Spores brown.
Spores elongate, septate3.*Phaeotrema Müll.-Arg.
Spores muriform4.*Leptotrema Mont.
Paraphyses scanty, branched.
Spores muriform, brown5.*Gyrostomum Fr.
Thallus with Phycopeltis gonidia6.*Phyllophthalmaria A. Zahlbr.
Apothecia in pseudostromata.
Apothecia united in tubercles7.*Tremotylium Nyl.
Apothecia united by the margins8.*Polystroma Clem.
XXVII. Diploschistaceae

Scarcely differing from the preceding family except in the gonidia which are Protococcaceous algae. The thallus is crustaceous and non-corticate. The apothecia have a double margin but the outer thalline margin is less overarching than in Thelotremaceae. The spores in the two genera are somewhat peculiar: in Conotrema they are exceedingly long and divided by parallel septa into thirty to forty small cells; in Diploschistes (Urceolaria) they are large, muriform and brown. Conotrema contains two corticolous species; Diploschistes about thirty species mostly saxicolous. Both genera are represented in the British Isles.

Spores elongate, multi-septate, colourless1. Conotrema Tuck.
Spores muriform, brown2. Diploschistes Norm.

XXVIII. Ectolechiaceae

A family of tropical epiphyllous lichens that are associated with Protococcaceous gonidia. The thallus is primitive in character, mostly a weft of hyphae with intermingled algal cells, described as homoiomerous.

The apothecia are without a thalline margin, and with a scarcely developed proper margin: their affinity is with the Lecideaceae, though in two genera, Lecaniella and Arthotheliopsis, there are gonidia below the hypothecium, a character of Lecanoraceae. The genera are nearly all monotypic; in Sporopodium has been included Lecidea phyllocharis Wainio (Sect. Gonothecium), which is distinguished by hymenial gonidia.

Apothecia at first covered by a “veil.”
Spores elongate, colourless, septate1.*Asterothyrium Müll.-Arg.
Apothecia uncovered from the first.
Gonidia not present below the hypothecium.
Paraphyses unbranched, free.
Spores muriform2.*Lopadiopsis Wain.
Paraphyses branched.
Spores 1-septate3.*Actinoplaca Müll.-Arg.
Spores elongate, multi-septate4.*Tapellaria Müll.-Arg.
Spores muriform5.*Sporopodium Mont.
Gonidia present below the hypothecium.
Spores elongate, 2-septate6.*Lecaniella Wain.
Spores muriform7.*Arthotheliopsis Wain.
XXIX. Gyalectaceae

The algal cells in this family are filamentous; either Myxophyceae (Scytonema) or Chlorophyceae (Trentepohlia or Phyllactidium). The thallus is crustaceous, and in some cases homoiomerous, as in Petractis, where the alga, Scytonema, penetrates the substratum as deeply as the hyphae. Monophiale, a tropical genus, possesses two kinds of gonidia: the species that grow on bark or mosses are associated with Trentepohlia; others that have invaded the surface of leathery evergreen leaves resemble most epiphyllous lichens in being associated with the leaf alga Phyllactidium (Phycopeltis). Some species of Trentepohlia exhale when moist an odour of violets. This scent is retained in at least one genus, Jonaspis.

The apothecia are superficial, and are soft, waxy and bright-coloured, with prominent margins which are however entirely hyphal: the affinity is therefore with Lecideaceae. In one genus, Sagiolechia, the fruit is carbonaceous and dark coloured. The spores of all the genera are colourless.

Apothecia waxy, bright-coloured.
Thallus with Scytonema gonidia.
Spores elongate, 3-septate1.Petractis Fr.
Thallus with Trentepholia gonidia.
Asci 6-8-spored.
Spores simple2.Jonaspis Th. Fr.
Spores 1-septate3.*Microphiale A. Zahlbr.
Spores septate or muriform4.Gyalecta Ach.
Asci 12-many-spored.
Spores 1-septate5.*Ramonia Stizenb.
Spores fusiform or acicular, many-septate6.Pachyphiale Lönnr.
Apothecia carbonaceous.
Spores elongate, 2-3-septate7.*Sagiolechia Massal.
XXX. Coenogoniaceae

There are only two genera in this small family, Coenogonium with Trentepohlia gonidia, and Racodium with Cladophora. Both genera follow the algal form and are filamentous. In Coenogonium the filaments are sometimes matted into a loose felted expansion. The genus is mainly tropical or subtropical and mostly rather light-coloured. There is only one British species, C. ebeneum[1050], a sterile form, in which the hyphae are very dark-brown; it often covers large areas of stone or rock with its sooty-like creeping filaments.

Racodium includes 2 (?) species. One of these, R. rupestre, is sterile and resembles C. ebeneum in form and colour.

The apothecia of Coenogonium are waxy and light-coloured; they are borne laterally on the filaments; the spores are simple or 1-septate.

Thallus with Trentepohlia gonidia1.Coenogonium Ehrenb.
Thallus with Cladophora gonidia2.Racodium Fr.
XXXI. Lecideaceae

One of the largest lichen families as regards both genera and species, and of world-wide distribution. The algal cells are Protococcaceae. The thallus is mostly crustaceous but it becomes squamulose in Psora, a section of Lecidea; and in Sphaerophoropsis, a Brazilian genus, there are small upright fronds or stalks with lateral apothecia. The prevailing colour of the thallus is some shade of grey, but it ranges from white or yellow to dark-brown or almost black. Cephalodia appear in some of the species.

The apothecia have a proper margin only, no gonidia taking part in the fruit-formation. They may be soft and waxy (biatorine) or hard and carbonaceous (lecideine). The genera are mainly based on spore characters which are very varied.

The arrangement of genera given below follows that of Zahlbruckner; in several instances, both as to the limitations of genera and to the nomenclature, it differs from that of British text-books, though the general principle of classification is the same.

Thallus crustaceous non-corticate.
Spores simple.
Spores small, thin-walled.
Spores colourless1.Lecidea Ach.
Spores brown2.*Orphniospora Koerb.
Spores large, thick-walled3.Mycoblastus Norm.
Spores 1-septate.
Spores small, thin-walled4.Catillaria Th. Fr.
Spores large, thick-walled5.Megalospora Mey. and Flot.
Spores elongate, 3-multi-septate.
Spores elongate, narrow, thin-walled6.Bacidia A. Zahlbr.
Spores elongate, large and thick-walled7.Bombyliospora De Not.
Spores muriform.
Spores colourless; on trees8.Lopadium Koerb.
Spores colourless to brown; on rocks9.Rhizocarpon Th. Kr.
Thallus warted or squamulose, corticate.
Spores elongate, 1-7-septate, thin-walled10.Toninia Th. Fr.
Thallus of upright podetia-like small fronds.
Spores ellipsoid, becoming 1-septate11.*Sphaerophoropsis Wain.
XXXII. Phyllopsoraceae

A small family of exotic lichens with a somewhat more developed thallus than that of the Lecideaceae, being in both of the genera squamulose or almost foliose.

The apothecia are without a thalline margin; they are biatorine or lecideine; the hypothecium is formed of plectenchyma and is purple-red in one species, Phyllopsora furfuracca. The two genera differ only in spore characters. There are fifteen species, mostly corticolous, belonging to Phyllopsora; only one, from New Zealand, is recorded for Psorella.

Spores simple1.*Phyllopsora Müll.-Arg.
Spores elongate, septate2.*Psorella Müll.-Arg.
XXXIII. Cladoniaceae

Associated with Lecideaceae in the type of apothecium, but differing widely in thallus formation. The latter is of a twofold type: the primary thallus is crustaceous, squamulose, or very rarely foliose; the secondary thallus or podetium, upright, simple or branched, is terminated by the apothecia, or broadens upwards to cup-like scyphi. Algal cells, Protococcaceae, according to Chodat, Cystococcus.

Much attention has been given to the origin and development of the podetia in this family. They are superficial on granule or squamule except in the monotypic Himalayan genus Gymnoderma where they are marginal on the large leaf-like lobes. Though in origin the podetia are doubtless fruit stalks, they have become in most cases vegetative in function.

The fruits are coloured yellowish, brown or red (or dark and carbonaceous in Pilophorus), and are borne on the tips of the branches or on the margins of the scyphi. In Glossodium and Thysanothecium—the former from New Granada, the latter from Australia—the apothecia occupy one side of the widened surface at the tips.

Cephalodia are developed on the primary thallus of Pilophorus, and on the podetia of Stereocaulon and Argopsis.

Podetia simple, short, not widening upwards.
Podetial stalks naked.
Primary thallus thin, continuous1.Gomphillus Nyl.
Primary thallus granular or squamulose2.Baeomyces Pers.
Primary thallus foliose.
Podetia superficial3.*Heteromyces Müll.-Arg.
Podetia marginal4.*Gymnoderma[1051] Nyl.
Podetial stalks granular, squamulose5.Pilophorus Th. Fr.
Podetia short, widening upwards.
Podetia simple above, rarely divided6.*Glossodium Nyl.
Podetia lobed, leaf-like7.*Thysanothecium Berk. & Mont.
Podetia elongate, variously branched, or scyphous and hollow8.Cladonia Hill.
Podetia elongate, not scyphous, the stalks solid.
Spores elongate, septate9.Stereocaulon Schreb.
Spores muriform10.*Argopsis Th. Fr.
XXXIV. Gyrophoraceae

A small family of foliose lichens allied to Lecideaceae by the character of the fruit—a superficial apothecium in the formation of which the gonidia take no share. There are only three genera, distinguished by differences in spore and other characters. Dermatiscum has light-coloured thallus and fruits; of the two species, one occurs in Central Europe, the other in North America. Umbilicaria and Gyrophora are British; they are dark-coloured rock-lichens and are extremely abundant in Northern regions where they are known as “tripe de roche.” Algal cells Protococcaceae.

Umbilicaria, Dermatiscum, and some species of Gyrophora are attached to the substratum by a central point. Other species of Gyrophora are rhizinose. In all there is a cortex of plectenchyma above and below. In Gyrophora the thallus may be monophyllous as in Umbilicaria, or polyphyllous and with or without rhizinae. New lobes frequently arise from protuberances or warts on the older parts of the thallus. At the periphery, in most species, growth is equal along the margins, in G. erosa[1052] the edge is formed of numerous anastomosing lobes with lateral branching, the whole forming a broadly meshed open network. Further back the tissues become continuous owing to the active growth of the lower tissue or hypothallus, which grows out from all sides and meets across the opening. The overlying layers, with gonidia, follow more slowly, but they also in time become continuous, so that the “erose” character persists only near the periphery. This forward growth of the lower thallus occurs in other species, though to a much less marked degree.

There is abundant detritus formation in this family; the outer layers of the cortex are continually being sloughed, the dead tissues lying on the upper surface as a dark gelatinous layer, continuous or in small patches. On the under surface the cast-off cortex gathers into a loose confused mass of dead tissues.

Asci 8-spored.
Spores mostly simple (disc gyrose)1.Gyrophora Ach.
Spores 1-septate2.*Dermatiscum Nyl.
Asci 1-2-spored.
Spores muriform3.Umbilicaria Hoffm.
XXXV. Acarosporaceae

Thallus foliose, squamulose or crustaceous, sometimes scarcely developed. Algal cells Protococcaceae.

Into this family Zahlbruckner has gathered the genera in which the asci are many-spored, as he considers that a character of great importance in determining relationship, but he has in doing so overlooked other very great differences. The fruit-bodies are round and completely enclosed in a thalline wall in Thelocarpon, which has however no perithecial wall. They have a proper margin only (lecideine) in Biatorella, and a thalline margin (lecanorine) in the remaining genera. In Acarospora the apothecia are sunk in the thallus. Stirton’s genus Cryptothecia[1053] is allied to Thelocarpon in the fruit-formation, but the basal thallus is well developed and the spores are few in number and variously divided.

Thallus none.
Apothecia (or perithecia) in thalline warts1.Thelocarpon Nyl.
Thallus crustaceous.
Apothecia lecideine; spores simple2.Biatorella Th. Fr.
Apothecia lecanorine; spores septate3.*Maronea Massal.
Thallus of small squamules4. Acarospora Massal.
Thallus almost foliose, attached centrally5.*Glypholecia Nyl.
XXXVI. Ephebaceae

A family of very simple structure either filamentous, foliose or crustaceous. The algal cells which give a dark colour to the thallus are Stigonema or Scytonema, members of the blue-green Myxophyceae, and consist of minute simple or branched filaments—single cell-rows in Scytonema, compound in Stigonema.

In some of the genera the lichen hyphae travel within the gelatinous sheath of the filaments, both algae and hyphae increasing by apical growth so that filaments many times the length of the alga are formed as in Ephebe. In others the filaments scarcely increase beyond the normal size of the alga as in Thermutis (Gonionema); or the gelatinous algal cells may be distributed in a stratum of hyphae.

The apothecia are minute and almost closed; they may be embedded in swellings of the thallus, or are more or less superficial. The spores are rather small, colourless and simple or 1-septate.

The lichens of this family are rock-dwellers and are mostly to be found in hilly or Alpine regions. A tropical species, Leptogidium dendriscum, occurs in sterile condition in south-west Ireland. There are few species in any of the genera.

Algal cells Scytonema.
Thallus minutely fruticose, non-corticate1.Thermutis Fr.
Thallus minute, of felted filaments,
cortex one cell thick2.*Leptodendriscum Wain.
Thallus of elongate filaments, cortex of
several cells3.Leptogidium Nyl.
Thallus foliose or fruticose,
cellular throughout4.Polychidium Ach.
Thallus crustaceous, non-corticate5.Porocyphus Koerb.
Algal cells Stigonema.
Thallus minutely fruticose, non-corticate6.Spilonema Born.
Thallus of long branching filaments.
Spores septate; paraphyses wanting7.Ephebe Fr.
Spores simple; paraphyses present8.Ephebeia Nyl.
Thallus crustaceous; upper surface
non-corticate, lower surface corticate9.*Pterygiopsis Wain.
XXXVII. Pyrenopsidaceae

In this family are included gelatinous lichens of which the gonidium is a blue-green alga with a thick gelatinous coat, either Gloeocapsa (including Xanthocapsa) or Chroococcus. In Gloeocapsa and Chroococcus the gelatinous envelope is often red, in Xanthocapsa it is yellow, and these colours persist more or less in the lichens, especially in the outer layers.

The thallus is in many cases a formless gelatinous crust of hyphal filaments mingling with colonies of algal cells as in Pyrenopsis; but small fruticose tufts are characteristic of Synalissa, and larger foliose and fruticose thalli appear in some exotic genera. A plectenchymatous cortex is formed on the thallus of Forssellia, a crustaceous genus from Central Europe, with two species only; the whole thallus is built up of a kind of plectenchyma in some others, but in most of the genera there is no tissue formed.

The apothecia, as in Ephebaceae, are generally half-closed.

Thallus with Gloeocapsa gonidia.
Thallus crustaceous.
Spores simple1.Pyrenopsis Nyl.
Spores 1-septate2.*Cryptothele Forss.
Thallus shortly fruticose3.Synalissa Fr.
Thallus lobate, centrally attached4.*Phylliscidium Forss.
Thallus with Chroococcus gonidia.
Thallus crustaceous5.Pyrenopsidium Forss.
Thallus lobate, centrally attached6.*Phylliscum Nyl.
Thallus with Xanthocapsa gonidia.
Thallus crustaceous.
Thallus non-corticate.
Spores simple.
Apothecia open, asci 8-spored7.Psorotichia Forss.
Apothecia covered, asci many-spored8.*Gonohymenia Stein.
Spores 1-septate.
Apothecia closed9.*Collemopsidium Nyl.
Thallus with plectenchymatous cortex10.*Forssellia A. Zahlbr.
Thallus lobate, centrally attached.
Spores simple.
Thallus plectenchymatous throughout11.*Anema Nyl.
Thalline tissue of loose hyphae12.*Thyrea Massal.
Cortex of upright parallel hyphae13.*Jenmania Wächt.
Spores 1-septate.
Thalline tissue of loose hyphae14.*Paulia Fée.
Thallus fruticose.
Thallus without a cortex15.*Peccania Forss.
Thallus with cortex of parallel hyphae16.*Phloeopeccania Stein.
XXXVIII. Lichinaceae

The only family of lichens associated with Rivularia gonidia, the trichomes of which retain their filamentous form to some extent in the more highly developed genera; they lie parallel to the long axis of the squamule or of the frond except in Lichinella in which genus they are vertical to the surface. The thallus may be crustaceous, or minutely foliose, or fruticose; in all cases it is dark-brown in colour, and the gelatinous character is evident in the moist condition. The best known British genus is Lichina which grows on rocks by the sea.

The apothecia are more or less immersed in the tissue; in Pterygium and Steinera they are open and superficial (the latter monotypic genus confined to Kerguelen). They are also open in Lichinella and Homopsella, both very rare genera. The spores are colourless and simple except in Pterygium and Steinera where they are elongate, and 1-3-septate.

Thallus crustaceous squamulose.
Apothecia immersed in thalline warts1.*Calothricopsis Wain.
Apothecia superficial, with thalline margin2.*Steinera A. Zahlbr.
Apothecia superficial, without a thalline margin3.Pterygium Nyl.
Thallus of small fruticose fronds.
Gonidia occupying the central strand4.*Lichinodium Nyl.
Gonidia not in the centre.
Apothecia immersed5.Lichina Ag.
Apothecia superficial.
Paraphyses present6.*Lichinella Nyl.
Paraphyses absent7.*Homopsella Nyl.
XXXIX. Collemaceae

The most important family of the gelatinous lichens and the most numerous. Collema is historically interesting as having first suggested the composite thallus. Algal cells, Nostoc, which retain the chain-like form except in Leprocollema, a doubtful member of the family. The thallus varies from indeterminate crusts to lobes of considerable size; occasionally the lobes are narrow and erect, forming minute fruticose structures. In the more primitive genera the thallus is non-corticate, but in the more evolved, the apical cells of the hyphae coalesce to form a continuous cellular cortex, one or more cells thick, well marked in some species, in others rudimentary; the formation of plectenchyma also occurs occasionally in the apothecial tissues of some non-corticate species.

The apothecia are superficial except in Pyrenocollema, a monotypic genus of unknown locality. They are generally lecanorine, with gonidia entering into the formation of the apothecium: in some genera they are lecideine or biatorine, being formed of hyphae alone. The spores are colourless and vary in form, size and septation.

Apothecia immersed; spores fusiform, 1-septate1.*Pyrenocollema Reinke.
Apothecia superficial.
Thallus without a cortex.
Spores simple, globose or ellipsoid.
Thallus crustaceous2.*Leprocollema Wain.
Thallus largely squamulose-fruticose.
Apothecia lecideine (dark-coloured)3.*Leciophysma Th. Fr.
Apothecia lecanorine4.Physma Massal.
Spores variously septate or muriform.
Apothecia biatorine (light-coloured)5.*Homothecium Mont.
Apothecia lecanorine6.Collema Wigg.
Thallus with cortex of plectenchyma.
Spores simple.
Spores globose7.Lemmopsis A. Zahlbr.
Spores ellipsoid, with thick subverrucose wall8.*Dichodium Nyl.
Spores vermiform, spirally curved9.*Koerberia Massal.
Spores variously septate or muriform.
Apothecia biatorine (light-coloured)10.*Arctomia Th. Fr.
Apothecia lecanorine11.Leptogium S. F. Gray.

XL. Heppiaceae

A family belonging to the “blue-green” series as it is associated with a gelatinous alga, Scytonema, but is of almost entirely cellular structure and is non-gelatinous. The thallus is squamulose or minutely foliose, or is formed of narrow almost fruticose lobes; the apothecia are semi-immersed; the asci are 4-many-spored.

Heppia is a wide-spread genus both in northern and tropical regions with about forty species that live on soil or rock. So far, no representative has been recorded in our Islands.

Spores simple, colourless, globose or ellipsoid1.*Heppia Naeg.
Spores muriform, colourless, ellipsoid2.*Amphidium[1054] Nyl.
XLI. Pannariaceae

The members of this family are also non-gelatinous, though for the most part associated with blue-green gelatinous algae, Nostoc or Scytonema. The gonidia are bright-green in the genera Psoroma and Psoromaria, the former often included under Lecanora, but too closely resembling Pannaria to be dissociated from that genus.

The thallus varies from being crustaceous to squamulose or foliose, and has a cortex of plectenchyma on the upper and sometimes also on the lower surface. The apothecia are superficial or lateral and with or without a thalline margin (lecanorine or biatorine), the spores are colourless.

Zahlbruckner has included Hydrothyria in this family. It is a monotypic aquatic genus found in North America and very closely allied to Peltigera. The British species of the genus, familiarly known as Coccocarpia, have been placed under Parmeliella, the former name being restricted to the tropical or subtropical species first assigned to Coccocarpia and distinguished by the cortex, the hyphae forming it lying parallel with the surface though forming a regular plectenchyma.

An Antarctic lichen Thelidea corrugata with Palmella gonidia is doubtfully included: the thallus is foliose, the apothecia biatorine with colourless 1-septate spores.

Thallus with bright-green gonidia.
With Palmella1.*Thelidea Hue.
With Protococcaceae.
Apothecia non-marginate (biatorine)2.*Psoromaria Nyl.
Apothecia marginate3.Psoroma Nyl.
Thallus with Scytonema gonidia.
Apothecia marginate, spores 1-septate4.Massalongia Koerb.
Apothecia non-marginate; spores simple.
Upper surface smooth5.*Coccocarpia Pers.
Upper surface felted6.*Erioderma Fée.
Thallus with Nostoc gonidia.
Apothecia marginate; spores simple7.Pannaria Del.
Apothecia non-marginate; spores various.
Thallus crustaceous or minutely squamulose8.Placynthium Ach.
Thallus squamulose, cortex indistinct9.*Lepidocollema Wain.
Thallus squamulose or foliose, cortex cellular10.Parmeliella Müll.-Arg.
Thallus foliose, thin veined below11.*Hydrothyria Russ.
XLII. Stictaceae

Thallus foliose, mostly horizontal, with a plectenchymatous cortex on both surfaces, a tomentum of hair-like hyphae taking the place of rhizinae on the lower surface. Algal cells Protococcaceae or Nostoc. Cephalodia and cyphellae or pseudocyphellae often present. Apothecia superficial or lateral; spores colourless or brown, variously septate.

The highly organized cortex and the presence of aeration organs—cyphellae or pseudocyphellae—which are almost solely confined to the genus Sticta give this family a high position as regards vegetative development. The two genera are of wide distribution, but Sticta is more abundant in the Southern Hemisphere. Lobaria pulmonaria is one of our largest lichens.

Under surface dotted with cyphellae or pseudocyphellae1. Sticta Schreb.
Under surface without these organs2. Lobaria Schreb.
XLIII. Peltigeraceae

A family of heteromerous foliose lichens containing in some instances blue-green (Nostoc), in others bright-green (Protococcaceae) gonidia, and thus representing a transition between these two series. They have large or small lobes and grow on the ground or on trees.

Cephalodia, either ectotrophic (Peltidea) or endotrophic (Solorina), occur in the family and further exemplify the capacity of the fungus hyphae to combine with different types of algae.

The upper surface is a wide cortex of plectenchyma, which in some forms (Nephromium) is continued below. In the non-corticate under surface of Peltigera, the lower hyphae grow out in hairs or rhizinae, very frequently brown in colour. Intercalary growth of the upper tissues stretches the thallus and tears apart the lower under surface so that the hair-bearing areas become a network of veins, with the white exposed medulla between. In Peltigera canina there is further growth and branching of the hyphae in the veins, adding to the bulk of the interlacing ridges.

From all other foliose lichens Peltigeraceae are distinguished by the flat wholly appressed or peltate apothecia without a thalline margin which arise mostly on the upper surface, but in Nephromium on the extreme margin of the under surface, the tip of the fertile lobe in that case is turned back as the apothecium matures, so that the fruit eventually faces the light. In Nephroma has been included Eunephroma with bright-green gonidia and Nephromium with blue-green.

Bitter[1055] has recorded the finding of apothecia on the under surface of Peltigera malacea and not at the margin, as in Nephromium. The plant was otherwise normal and healthy. Solorinella, from Central Europe and Asteristion from Ceylon are monotypic genera with poorly developed thalli.

Thallus poorly developed.
Asci 6-8-spored; spores 3-5-septate1.*Asteristion Leight.
Asci many-spored; spores 1-septate2.*Solorinella Anzi.
Thallus generally well developed.
Apothecia superficial, sunk in the thallus3.Solorina Ach.
Apothecia terminal on upper surface of lobes4.Peltigera Willd.
Apothecia terminal on lower surface of lobes5.Nephroma Ach.
XLIV. Pertusariaceae

Thallus crustaceous, often rather thick and with an amorphous cortex on the upper surface. Algal cells Protococcaceae. Apothecia solitary or several immersed in thalline warts, generally with a narrow opening which barely exposes the disc, and which in one genus, Perforaria, is so small as almost to constitute a perithecium; spores are often very large and with thick walls; some if not all are multinucleate and germinate at many points.

In the form of the fruit, this family stands between Pyrenocarpeae and Gymnocarpeae, though more akin to the latter. Perforaria, with two species, belongs to New Zealand and Japan. Pertusaria has a world-wide distribution, and Varicellaria, a monotypic genus, with a very large two-celled spore, is an Alpine plant, recorded from Europe and from Antarctic America.

Spores simple.
Apothecia with pore-like opening1.*Perforaria Müll.-Arg.
Apothecia with a wider opening2.Pertusaria DC.
Spores 1-septate3. Varicellaria Nyl.
XLV. Lecanoraceae

Thallus mostly crustaceous, occasionally squamulose or very rarely minutely fruticulose. The squamulose thallus is corticate above, the under surface appressed and attached to the substratum by penetrating hyphae, often effigurate at the circumference. Algal cells Protococcaceae. Apothecia well distinguished by the thalline margin; spores colourless, simple or variously septate or muriform.

Lecanora, Ochrolechia, Lecania, Haematomma and Phlyctis are cosmopolitan genera, some of them with a very large number of species; the other genera are more restricted in distribution and generally with few species.

The genus Candelariella is of uncertain position; the spores are 8 or many in the ascus and are simple or 1-septate, and not unfrequently become polarilocular as in Caloplacaceae, but there is no parietin present.

Algae distributed through the thallus. Spores simple1.*Harpidium Koerb.
Algae restricted to a definite zone.
Spores simple.
Thallus grey, white or yellowish.
Spores rather small2.Lecanora Ach.
Spores large3.Ochrolechia Massal.
Thallus bright yellow.
Spores simple or 1-septate4.Candelariella Müll.-Arg.
Spores 1-septate (rarely pluri-septate).
Paraphyses free.
Thallus squamulose, effigurate5.Placolecania Zahlbr.
Thallus crustaceous.
Apothecial disc brownish6.Lecania Zahlbr.
Apothecial disc flesh-coloured7.Icmadophila Trevis.
Paraphyses branched, intricate8.*Calenia Müll.-Arg.
Spores elongate, pluri-septate.
Apothecia superficial9.Haematomma Massal.
Apothecia immersed.
Paraphyses free10.*Phlyctella Müll.-Arg.
Paraphyses branched, intricate11.*Phlyctidia Müll.-Arg.
Spores muriform.
Apothecia superficial12.*Myxodictyon Massal.
Apothecia immersed13.Phlyctis Wallr.
XLVI. Parmeliaceae

A very familiar family of foliose lichens. Genera and species are dorsiventral and stratose in structure, though some Cetrariae are fruticose in habit. Algal cells are Protococcaceae; in Physcidia they are Palmellae. In every case the upper surface of the thallus is corticate and generally of plectenchyma, the lower being somewhat similar, but in Heterodea and Physcidia, monotypic Australasian genera, the upper cortex is of branching hyphae parallel with the surface, the lower surface being non-corticate.

The Parmeliae are mostly provided with abundant rhizinae; in Cetrariae and Nephromopsis these are very sparingly present, while in Anzia (including Pannoparmelia) the medulla passes into a wide net-like structure of anastomosing hyphae.

In Heterodea, cyphellae occur on the under surface as in Stictaceae; and in Cetraria islandica bare patches have been described as pseudocyphellae. The latter lichen is one of the few that are of value as human food. Special aeration structures are present on the upper cortex of Parmelia aspidota.

Thallus non-corticate below.
Apothecia terminal1.*Heterodea Nyl.
Apothecia superficial2.*Physcidia Tuck.
Thallus spongy below3.*Anzia Stizenb.
Thallus corticate below.
Asci poly-spored4.Candelaria Massal.
Asci 8-spored.
Spermatia acrogenous5.Parmeliopsis Nyl.
Spermatia pleurogenous.
Apothecia superficial6.Parmelia Ach.
Apothecia lateral.
Apothecia on upper surface7.Cetraria Ach.
Apothecia on lower surface8.*Nephromopsis Müll.-Arg.
XLVII. Usneaceae

This also is a familiar family of lichens, Usnea barbata the “bearded moss” being one of the first lichens noted and chronicled. Algal cells Protococcaceae. Structure radiate, the upright or pendulous habit characteristic of the family securing all-round illumination. Special adaptations of the cortex or of the internal tissues have been evolved to strengthen the thallus against the strains incidental to their habit of growth as they are attached in nearly all cases by one point only, by a special sheath, or by penetrating hold-fasts.

Apothecia are superficial or marginal and sometimes shortly stalked; spores are simple or variously septate.

Ramalina and Usnea, the most numerous, are cosmopolitan genera; Alectoria inhabits northern or hilly regions.

The genus Evernia, also cosmopolitan, represents a transition between foliose and fruticose types; the fronds of the two species, though strap-shaped and generally upright, are dorsiventral and stratose, the gonidia for the most part lying beneath one surface; the other (lower) surface is either white or very dark-coloured. Everniopsis, formed of thin branching strap-shaped fronds, is also dorsiventral.

A number of genera, Thamnolia, Siphula, etc. are of podetia-like structure, generally growing in swards. Several of them have been classified with Cladoniae, but they lack the double thallus. One of these, Endocena, a sterile monotypic Patagonian lichen, with stiff hollow coralloid fronds, was classified by Hue[1056] along with Siphula; recently he has transferred it to his family Polycaulionaceae[1057] based on Polycauliona regale (Placodium frustulosum Darbish.), and allied to Placodium Sect. Thamnoma[1058]. In recent studies Hue has laid most stress on thalline characters. He places the new family between “Ramalinaceae” and “Alectoriaceae.” Dactylina arctica is a common Arctic soil-lichen.

Thallus strap-shaped.
Structure dorsiventral.
Greyish-green above1.Evernia Ach.
Whitish-yellow above2.*Everniopsis Nyl.
Structure radiate alike on both surfaces.
Fronds grey; medulla of loose hyphae3.Ramalina Ach.
Fronds yellow; medulla traversed by strands4.*Letharia A. Zahlbr.
Thallus filamentous.
Medulla a strong “chondroid” strand5.Usnea Dill.
Medulla of loose hyphae.
Spores simple6.Alectoria Ach.
Spores muriform, brown7.*Oropogon Fr.
Thallus of upright podetia-like fronds.
Fronds rather long (about two inches), tapering, white8.Thamnolia Ach.
(Cerania S. F. Gray).
Fronds shorter, blunt.
Medulla solid9.*Siphula Fr.
Medulla partly or entirely hollow.
Fronds swollen and tall (about two inches)10.*Dactylina Nyl.
Fronds coralloid, entangled11.*Endocena Cromb.
Fronds short, upright12.*Dufourea Nyl.
XLVIII. Caloplacaceae

In this family Zahlbruckner has included the squamulose or crustaceous lichens with colourless polarilocular spores, relegating those with more highly developed thallus or with brown spores to other families. He has also substituted the name Caloplaca for the older Placodium, the latter being, as he considers, less well defined.

Algal cells are Protococcaceae. The thallus is mostly light-coloured, generally some shade of yellow, and, with few exceptions, contains parietin, which gives a purple colour on the application of potash. The squamulose forms are closely appressed to the substratum, and have often a definite rounded outline (effigurate). The spores have a thick median septum with a loculus at each end and a connecting canal[1059].

In Blastenia the outer thalline margin is obscure or absent—though gonidia are frequently present below the hymenium. Caloplacaceae occur all over the globe; they are among the most brilliantly coloured of all lichens. Polycauliona Hue[1060] possibly belongs here: though based on thalline rather than on spore characters, one species at least has polarilocular spores.

Apothecia with a distinct thalline margin1. Caloplaca Th. Fr.
Apothecia without a thalline margin2. Blastenia Th. Fr.

XLIX. Teloschistaceae

Polarilocular colourless spores are the distinguishing feature of this family as of the Caloplacaceae. Algal cells Protococcaceae. The thallus of Teloschistaceae is more highly developed, being either foliose or fruticose, though never attaining to very large dimensions. The cortex of Xanthoria (foliose) is plectenchymatous, that of Teloschistes (fruticose) is fibrous. The species of both genera are yellow or greenish-yellow due to the presence of the lichen-acid parietin.

Both genera have a wide distribution over the globe, more especially in maritime regions.

Thallus foliose1. Xanthoria Th. Fr.
Thallus fruticose2. Teloschistes Norm.
L. Buelliaceae

A family of crustaceous lichens distinguished by the brown two-celled spores. Algal cells Protococcaceae. Zahlbruckner has included here Buellia and Rinodina; the former with a distinctly lecideine fruit and with thinly septate spores; the latter lecanorine and with spores of the polarilocular type, with a very wide central septum pierced in most of the species by a canal which may or may not traverse the middle lamella of the wall. Rinodina is closely allied to Physciaceae, while Buellia has more affinity with Lecideaceae and is near to Rhizocarpon.

Both genera are of world-wide distribution.

Apothecia lecideine, without a thalline margin1. Buellia De Not.
Apothecia lecanorine, with a thalline margin2. Rinodina Massal.
LI. Physciaceae

Thallus foliose or partly fruticose, and generally attached by rhizinae. Algal cells Protococcaceae. The spores resemble those of Rinodina, dark-coloured with a thick septum and reduced cell-lumina. As in that species there may be a second septum in each cell, giving a 3-septate spore; but that is rare.

Pyxine, a tropical or subtropical genus, is lecanorine only in the very early stages; it soon loses the thalline margin. Anaptychia is differentiated from Physcia by the subfruticose habit, though the species are nearly all dorsiventral in structure, only a few of them being truly radiate and corticate on both surfaces. The upper cortex of Anaptychia is fibrous, but that character appears also in most species of Physcia either on the upper or the lower side. Physcia and Anaptychia are widely distributed.

Thalline margin absent in apothecia1.*Pyxine Nyl.
Thalline margin present in apothecia.
Thallus foliose2.Physcia Schreb.
Thallus fruticose3.Anaptychia Koerb.

C. *Hymenolichens

Fungus a Basidiomycete, akin to Thelephora. Algal cells Scytonema or Chroococcus. Thallus crustaceous, squamulose or foliose. Spores colourless, produced on basidia, on the under surface of the free thallus.

The Hymenolichens[1061] are few in number and are endemic in tropical or warm countries. They inhabit soil or trees.

Thallus of extended lobes.
Gonidia near the upper surface1.*Dictyonema Zahlbr.
Gonidia in centre of tissue2.*Cora Fr.
Thallus squamulose, irregular3.*Corella Wain.