Chapter VIII · SYSTEMATIC (continued 2)

A marked difference as regards species is noted between the Flora of Minnesota and that of California. Herre[1080] has directed attention to the great similarity between the lichens of the latter state and those of Europe: many European species occur along the coast and nowhere else in America so far as is yet known; as examples he cites, among others, Calicium hyperellum, Lecidea quernea, L. aromatica, Gyrophora polyrhiza, Pertusaria amara, Roccella fuciformis, R. fucoides and R. tinctoria. The Scandinavian lichen, Letharia vulpina, grows abundantly there and fruits freely; it is very rare in other parts of America. Herre found, however, no specimens of Cladonia rangiferina, Cl. alpestris or Cl. sylvatica, nor any species of Graphis; he is unable to explain these anomalies in distribution, but he considers that the cool equable climate is largely responsible: it is so much more like that of the milder countries of Europe than of the states east of the Sierra Nevada. His contention is supported by a consideration of Japanese lichens. With a somewhat similar climate there is a great preponderance of European forms. Out of 382 species determined by Nylander[1081], 209 were European. There were 17 Graphideae, 31 Parmeliae, and 23 Cladoniae, all of the last named being European. These results of Nylander’s accord well with a short list of 30 species from Japan compiled by Müller[1082] at an earlier date. They were chiefly crustaceous tree-lichens; but the Cladoniae recorded are the familiar British species Cl. fimbriata, Cl. pyxidata and Cl. verticillata.

With the Japanese Flora may be compared a list[1083] of Maingay’s lichens from China, 35 in all. Collema limosum, the only representative of Collemaceae in the list, is European, as are the two species of Ramalina, R. gracilenta and R. pollinaria; four species of Physcia are European, the remaining Ph. picta being a common tropical or subtropical plant. Lecanora saxicola, L. cinerea, Placodium callopismum and Pl. citrinum are cosmopolitan, other Lecanorae and most of the Lecideae are new. Graphis scripta, Opegrapha subsiderella and Arthonia cinnabarina—the few Graphideae collected—are more or less familiar home plants. Among the Pyrenocarpei, Verrucaria (Pyrenula) nitida occurs; it is a widely distributed tree-lichen.

It is unnecessary to describe in detail the British lichens. Some districts have been thoroughly worked, others have barely been touched. The flora as a whole is of a western European type showing the influence of the Gulf Stream, though there is also a representative boreal growth on the moorlands and higher hills, especially in Scotland. Such species as Parmelia pubescens, P. stygia and P. alpicola recall the Arctic Circle while Alectoriae, Cetrariae and Gyrophorae represent affinity with the colder temperate zone.

In the southern counties such species as Sticta aurata, S. damaecornis, Phaeographis Lyellii and Lecanora (Lecania) holophaea belong to the flora of the Atlantic seaboard, while in S.W. Ireland the tropical genera Leptogidium and Anthracothecium are each represented by a single species. The tropical or subtropical genus Coenogonium occurs in Great Britain and in Germany, with one sterile species, C. ebeneum. Enterographa crassa is another of our common western lichens which however has travelled eastwards as far as Wiesbaden. Roccella is essentially a maritime genus of warm climates: two species, R. fuciformis and R. fucoides, grow on our south and west coasts. The famous R. tinctoria is a Mediterranean plant, though it is recorded also from a number of localities outside that region and has been collected in Australia.

In the temperate zones of the southern hemisphere are situated the great narrowing projections of South Africa and South America with Australia and New Zealand. As we have seen, the Antarctic flora prevails more or less in the extreme southern part of America, and the similarity between the lichens of that country and those of New Zealand is very striking, especially in the fruticulose forms. There is a very abundant flora in the New Zealand islands with their cool moist climate and high mountains. Churchill Babington[1084] described the collections made by Hooker. Stirton[1085] added many species, among others Calycidium cuneatum, evidently endemic. Later, Nylander[1086] published the species already known, and Hellbom[1087] followed with an account of New Zealand lichens based on Berggsen’s collections; many more must be still undiscovered. Especially noticeable as compared with the north, are the numbers of Stictaceae which reach their highest development of species and individuals in Australasia. They are as numerous and as prominent as are Gyrophoraceae in the north. A genus of Parmeliaceae, Hetorodea, which, like the Stictae, bears cyphellae on the lower surface, is peculiar to Australia.

A warm current from the tropical Pacific Ocean passes southwards along the East Coast of Australia, and Wilson[1088] has traced its influence on the lichens of Australia and Tasmania to which countries a few tropical species of Graphis, Chiodecton and Trypethelium have migrated. Various unusual types are to be found there also: the beautiful Cladonia retepora (Fig. 71), which spreads over the ground in cushion-like growths, with the genera Thysanothecium and Neophyllis, genera of Cladoniaceae endemic in these regions.

The continent of Africa on the north and east is in so close connection with Europe and Asia that little peculiarity in the flora could be expected. In comparing small representative collections of lichens, 37 species from Egypt and 20 from Palestine, Müller[1089] found that there was a great affinity between these two countries. Of the Palestine species, eight were cosmopolitan; among the crustaceous genera, Lecanorae were the most numerous. There was no record of new genera.

The vast African continent—more especially the central region—has been but little explored in a lichenological sense; but in 1895 Stizenberger[1090] listed all of the species known, amounting to 1593, and new plants and new records have been added since that day. The familiar genera are well represented, Nephromium, Xanthoria, Physcia, Parmelia, Ramalina and Roccella, some of them by large and handsome species. In the Sahara Steiner[1091] found that genera with blue-green algae such as the Gloeolichens were particularly abundant; Heppia and Endocarpon were also frequent. Algeria has a Mediterranean Flora rather than tropical or subtropical. Flagey[1092] records no species of Graphis for the province of Constantine, and only 22 species of other Graphideae. Most of the 519 lichens listed by him there are crustaceous species. South America stretches from the Tropics in the north to Antarctica in the south. Tropical conditions prevail over the central countries and tropical tree-lichens, Graphidaceae, Thelotremaceae, etc. are frequent; further West, on the Pacific slopes, Usneae and Ramalinae hang in great festoons from the branches, while the foliose Parmeliae and Stictae grow to a large size on the trunks of the trees.

Wainio’s[1093] Lichens du Brésil is one of the classic systematic books and embodies the writer’s views on lichen classification. There are no new families recorded though a number of genera and many species are new, and, so far as is yet known, these are endemic. Many of our common forms are absent; thus Peltigera is represented by three species only, P. leptoderma, P. spuriella and P. Americana, the two latter being new species. Sticta (including Stictina) includes only five species, and Coenogonium three. There are 39 species of Parmelia with 33 of Lecanora and 68 of Lecidea, many of them new species.

D. Lichens of Tropical Regions

In the tropics lichens come under the influence of many climates: on the high mountains there is a region of perpetual snow, lower down a gradual change to temperate and finally to tropical conditions of extreme heat, and, in some instances, extreme moisture. There is thus a bewildering variety of forms. By “tropical” however the warmer climate is always implied. Several families and genera seem to flourish best in these warm moist conditions and our familiar species grow there to a large size. Among crustaceous families Thelotremaceae and Graphidaceae are especially abundant, and probably originated there. In the old comprehensive genus Graphis, 300 species were recorded from the tropics. It should be borne in mind that Trentepohlia, the alga that forms the gonidia of these lichens, is very abundant in the tropics. Coenogonium, a genus containing about twelve species and also associated with Trentepohlia, is scarcely found in Europe, except one sterile species, C. ebeneum. Other species of the genus have been recorded as far north as Algeria in the Eastern Hemisphere and Louisiana in the Western, while one species, C. implexum, occurs in the southern temperate zone in Australia and New Zealand.

Of exclusively tropical lichens, the Hymenolichens are the most noteworthy. They include three genera, Cora, Corella and Dictyonema, the few species of which grow on trees or on the ground both in eastern and western tropical countries.

Other tropical or subtropical forms are Oropogon loxensis, similar to Alectoria in form and habit, but with one brown muriform spore in the ascus; it is only found in tropical or subtropical lands. Physcidia Wrightii (Parmeliaceae) is exclusively a Cuban lichen. Several small genera of Pyrenopsidaceae such as Jenmania (British Guiana), Paulia (Polynesia) and Phloeopeccania (South Arabia) seem to be confined to very hot localities. On the other hand Collemaceae are rare: Wainio records from Brazil only four species of Collema, with nine of Leptogium.

Among Pyrenolichens, Paratheliaceae, Mycoporaceae and Astrotheliaceae are almost exclusively of tropical distribution, and finally the leaf lichens with very few exceptions. These follow the leaf algae, Mycoidea, Phycopeltis, etc., which are so abundant on the coriaceous long-lived green leaves of a number of tropical Phanerogams. All the Strigulaceae are epiphytic lichens. Phyllophthalmaria (Thelotremaceae) is also a leaf genus; one of the species, Ph. coccinea, has beautiful carmine-red apothecia. The genera of the tropical family Ectolechiaceae also inhabit leaves, but they are associated with Protococcaceae; one of the genera Sporopodium[1094] is remarkable as having hymenial gonidia. Though tropical in the main, epiphyllous lichens may spread to the regions beyond: Sporopodium Caucasium and a sterile Strigula were found by Elenkin and Woronichin[1095] on leaves of Buxus sempervirens in the Caucasus, well outside the tropics.

Pilocarpon, an epiphytic genus, is associated with Protococcaceae; one of the species, P. leucoblepharum, spreads from the bark to the leaves of pine-trees; it is widely distributed and has also been reported in the Caucasus[1096]. Chrysothrix, in which the gonidia belong to the algal genus Palmella, grows on Cactus spines in Chili, and may also rank as a subtropical epiphyllous lichen.

A series of lichens from the warm temperate region of Transcaucasia investigated by Steiner[1097] were found to be very similar to those of Central Europe. Lecanoraceae were, however, more abundant than Lecideaceae and Verrucariaceae were comparatively rare.

Much of Asia lies within tropical or subtropical influences. Several regions have received some amount of attention from collectors. From Persia there has been published a list of 59 species determined by Müller[1098]; several of them are Egyptian or Arabian plants, 15 are new species, but the greater number are European.

A small collection of 53 species from India, near to Calcutta, published by Nylander[1099], included a new genus of Caliciaceae, Pyrgidium (P. bengalense), allied to Sphinctrina. He also recorded Ramalina angulosa in African species, along with R. calicaris, R. farinacea and Parmelia perlata, f. isidiophora, which are British. Other foliose forms, Physcia picta, Pyxine Cocoës and P. Meissnerii are tropical or subtropical; along with these were collected crustaceous tropical species belonging to Lecanorae, Lecideae, Graphideae, etc.

Leighton[1100] published a collection of Ceylon lichens and found that Graphideae predominated. Nylander[1101] came to the same conclusion with regard to lichens referred to him: out of 159 species investigated from Ceylon, there were 36 species of Graphideae. In another list[1102] of Labuan, Singapore and Malacca lichens, 164 in all, he found that 56 belonged to the Graphidei, 36 to Pyrenocarpei, 14 to Thelotremei and 11 to Parmelei; only 15 species were European.

On the whole it is safe to conclude from the above and other publications that the exceptional conditions of the tropics have produced many distinctive lichens, but that a greater abundance both of species and individuals is now to be found in temperate and cold climates.

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.