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.