III. FOSSIL LICHENS
In pronouncing on the great antiquity of lichens, proof has been adduced from physiological rather than from phytogeological evidence. It would have been of surpassing interest to trace back these plants through the ages, even if it were never possible to assign to any definite period the first symbiosis of the fungus and alga; but among fossil plants there are only scanty records of lichens and even these few are of doubtful determination.
The reason for this is fairly obvious: not only are the primitive thalline forms too indistinct for recognizable preservation, but all lichens are characterized by the gelatinous nature of the hyphal or of the algal membranes which readily imbibe water. They thus become soft and flaccid and unfit to leave any impress on sedimentary rocks. It has also been pointed out by Schimper[1103] that while deciduous leaves with fungi on them are abundant in fossil beds, lichens are entirely wanting. These latter are so firmly attached to the rocks or trees on which they grow that they are rarely dislodged, and form no part of wind- or autumn-fall. Trunks and branches of trees lose their bark by decay long before they become fossilized and thus all trace of their lichen covering disappears.
The few records that have been made are here tabulated in chronological order:
1. Palaeozoic. Schimper decides that there are no records of lichens in the earlier epochs. Any allusions[1104] to their occurrence are held to be extremely vague and speculative.
2. Mesozoic. Braun[1105] has recorded a Ramalinites lacerus from the Keuper sandstone at Eckersdorf, though later[1106] he seemed to be doubtful as to his determination. One other lichen, an Opegrapha, has been described[1107] from the chalk at Aix.
3. Cainozoic. In the brown-coal formations of Saxony Engelhardt[1108] finds two lichens: Ramalina tertiaria, a much branched plant, the fronds being flat and not channelled “and of further interest that it is attached to a carbonized stem.” The second form, Lichen dichotomus, has a dichotomously branching strap-shaped frond. “There is sufficient evidence that these fronds were cylindrical and that the width is due to pressure. In one place a channel is visible, filled with an ochraceous yellow substance.”
Other records on brown coal or lignite are: Verrucarites geanthricis[1109] Goepp., somewhat similar to Pyrenula nitida, found at Muskau in Silesia; Opegrapha Thomasiana[1110] Goepp., near to Opegrapha varia, and Graphis scripta succinea Goepp.[1111] on a piece of lignite in amber beds, all of them doubtful.
Schimper has questioned, as he well might, Ludwig’s[1112] records from lignite from the Rhein-Wetterau Tertiary formations; these are: Cladonia rosea, Lichen albineus, L. diffissus and L. orbiculatus; he thinks they are probably fungus mycelia. Another lichen, a Parmelia with apothecia, which recalls somewhat P. saxatilis or P. conspersa, collected by Geyler also in the brown coal of Wetterau is accepted by Schimper[1113] as more trustworthy.
More authentic also are the lichens from the amber beds of Königsberg and elsewhere collected by Goeppert and others. These deposits are Cainozoic and have been described by Goeppert and Menge[1114] as middle Miocene. Schimper gives the list as: Parmelia lacunosa Meng. and Goepp., fragments of thallus near to P. saxatilis; Sphaerophorus coralloides; Cladonia divaricata Meng. and Goepp.; Cl. furcata; Ramalina calicaris vars. fraxinea and canaliculata; Cornicularia aculeata, C. subpubescens Goepp., C. ochroleuca, C. succinea Goepp., and Usnea barbata var. hirta. Schimper rather deprecates specific determinations when dealing with such imperfect fragments.
In a later work Goeppert and Menge[1114] state that they have found twelve different amber lichens and that among these are Physcia ciliaris, Parmelia physodes and Graphis (probably G. scripta succinea) along with Peziza resinae which is more generally classified among lichens as Lecidea (Biatorella) resinae.
Another series of lichens found in recent deposits in North Europe has been described by Sernander[1115] as “subfossil.” While engaged on the investigations undertaken by the Swedish Turf-Moor Commission, he noted the alternation of slightly raised Sphagnum beds with lower-lying stretches of Calluna and lichen moor—in some instances dense communities of Cladonia rangiferina. In time the turf-forming Sphagnum overtopped and invaded the drier moorland, covering it with a new formation of turf. Beneath these layers of “regenerated turf” were found local accumulations of blackened remains of the Cladonia still recognizable by the form and branching. Some specimens of Cetraria islandica were also determined.
Of especial lichenological interest in these northern regions was the Calcareous Tufa or Calc-sinter in which Sernander also found subfossil lichens—distinct impressions of Peltigera spp. and the foveolae of endolithic calcicolous species.
In another category he has placed Ramalina fraxinea, Graphis sp. and Opegrapha sp., traces of which were embedded with drift in the Tufa. In the two Graphideae the walls of apothecia and pycnidia were preserved. Sernander considers their presence of interest as testifying to warmer conditions than now prevail in these latitudes.