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.