c. Mountain Lichens. On the mountain summits of our own and other lands are to be found lichens very similar to those of the far North the climatic conditions being the chief factors of importance in determining the formations. These regions are occupied by what Wheldon and Wilson[1198] describe as “a zone of Arctic-Alpine vegetation,” and they have recorded a series of lichen associations belonging to that zone on the schistose summits of the Perthshire mountains. The following is one of the most typical:
- Euopsis granatina.
- Sphaerophorus coralloides.
- Sphaerophorus fragilis.
- Gyrophora polyphylla.
- Cetraria tristis.
- Cetraria nivalis.
- Lecanora tartarea var. frigida.
- Lecanora upsaliensis.
- Aspicilia oculata.
- Pertusaria dactylina.
- Pertusaria glomerata.
- Stereocaulon denudatum.
- Parmelia saxatilis.
- Parmelia omphalodes.
- Parmelia lanata.
- Parmelia stygia.
- Stereocaulon tomentosum.
- Stereocaulon alpinum.
- Cladonia coccinca.
- Cladonia gracilis.
- Cladonia uncialis.
- Cladonia destricta.
- Cladonia racemosa.
- Lecidea arctica.
- Parmelia alpicola.
- Cetraria aculeata.
- Cetraria crispa.
- Cetraria islandica.
- Lecidea limosa.
- Lecidea alpestris.
- Lecidea demissa.
- Lecidea uliginosa.
- Lecidea cuprea.
- Lecidea Berengeriana.
- Lecidea cupreiformis.
- Lecidea atrofusca.
Again on the summit of Ben-y-Gloe the same authors[1199] have recorded Gyrophora erosa, G. torrefacta and G. cylindrica, Parmelia alpicola, Lecanora tartarea var. frigida, Lecidea limosa and L. arctica, the last two lichens thriving in the most bleak and exposed situations. Cladonia cervicornis grew in reduced squamulose cushions; Stereocaulon and Sphaerophorus in very compact forms, the outer stalks prostrate, the next inclined, the central ones erect so that points only are exposed and no lateral stress is caused by wind storms. Erect fruticose lichens are absent in this region, being represented only by Parmelia lanata, a semi-decumbent plant, and by Thamnolia vermicularis which is prostrate on the ground except where the points of the stalks turn up to catch the dew. Many of the Lecideae were observed to have large fruits and very little thallus: “the hyphae ramify in the minute interstices of the stone and the gonidia cluster under the lea of the apothecia: this is especially the case on loose stones where conditions are extremely dry.”
On the Continent an interesting study of the lichens of high altitudes was made by Maheu[1200] in the Savoyard Oberland. On the Great Casse at a height of 3861 m. he collected four mosses and sixteen lichens. These were:
- Stereocaulon condensatum.
- Gyrophora cylindrica.
- Gyrophora spodochroa.
- Solorina crocea.
- Solorina saccata.
- Parmelia encausta.
- Candelaria concolor.
- Caloplaca pyracea var. nivalis.
- Haematomma ventosum.
- Acarospora smaragdula.
- Psora decipiens.
- Buellia discolor.
- Buellia stellulata.
- Lecidea contigua var. steriza.
- Lecidea confluens.
- Dermatocarpon hepaticum.
He found that as he climbed higher and higher foliaceous species became rarer and crustaceous more abundant. The colour of the lichens on the high summits was slightly weakened and the thallus often reduced, but all were fertile and the apothecia normal and sporiferous. Lichens at less high altitudes where they emerge from the snow covering for longer periods and enjoy light and sunshine are, as already observed, often very brightly coloured and of luxuriant growth.
d. Tundra Lichens. In phyto-geography the term “tundra” is given to great stretches of country practically treeless and unsheltered within the Polar climate; the tundra extends from the zone of dwarfed trees on to the permanent ice or snow fields. The vegetation includes a few dwarfed trees, shrubs, etc., but is mainly composed of mosses and lichens; the latter being the most abundant. These are true climatic lichen formations.
Leighton[1201], in describing lichens from Arctic America brought home by the traveller, Sir John Richardson, quotes from the latter that: “the terrestrial lichens were gathered on Great Bear, and Great Slave Lakes before starting on our summer voyages after the snow had melted.... The barren grounds are densely covered for many hundreds of miles with Corniculariae and Cetrariae, and where the ground is moist with Cladoniae, while the boulders thickly scattered over the surface are clothed with Gyrophorae.... The smaller stones on the gravelly ridges of the Barren Grounds are covered with lichens.”
The accounts of tundra lichens that have been given by various travellers deal chiefly with the more prominent terricolous forms. They have been classified as “Cladina tundra,” including Cladonia rangiferina and Sphaerophorus coralloides, “Cetraria tundra,” and “Alectoria heath,” the latter the hardiest of all. Great swards of these lichens often alternate with naked stony soil.
Kihlman[1202] has noted, as characteristic of tundra formations, the compact cushion-like growth of the mosses which are thus enabled to store up water and to conduct it by capillarity throughout the mass to the highest stalks. Certain tundra lichens take on the same growth character as adaptations to the strenuous life conditions. Cetraria glauca f. spadicea with f. congesta and C. crispa are examples of this compact growth: they form a soft thick carpet of a yellowish-grey colour. Cladoniae also grow in crowded tufts, but are generally to be found in the more sheltered positions, in valleys between the tundra hills and in the clefts of the rocks, or between great boulders and stones where there is also more moisture.