While in a higher position on similar boulders:

And more rarely a few species of Lecidea.

b. Lichens of Sand-dunes. These lichens might be included with those of the terricolous communities, but they really represent a maritime community of xerophytic type, subject to the influence of salt spray but not within reach of the tide. They are sun-lichens and react to the strong light in the deeper colour of the thallus. In such a sun-baked area at Findhorn a luxuriant association of lichens was observed growing among short grass and plant debris. It consisted chiefly of:

On very arid situations the species of Cladonia are those that have a well-developed rather thick primary thallus, probably because such a thallus is able to retain moisture for a prolonged period[1193]. On shifting sand, as in the desert, there are no lichens; it is only on surfaces more or less fixed by marram grass that lichens begin to develop, though in the cool damp weather of autumn and winter, as observed by Wheldon and Wilson[1194], certain species associated with Myxophyceae, such as Collemaceae, may make their appearance, among others Leptogium scotinum, Collemodium turgidum and Collema ceranoides. Watson[1195] makes the same observation in his study of sand-dunes.

When the loose sand on the dunes of South Lancashire becomes cemented by algae and mosses several rare Lecideae are to be found on the decaying vegetation, and with further accumulation of humus Cladoniae appear and spread rapidly along with several species of Peltigera and the ubiquitous Parmelia physodes. The latter starts on dead twigs of Salix repens and spreads on to the surrounding soil where it forms patches some inches in diameter. The association also includes Lecidea uliginosa and Bilimbia sphaeroides.

On the more inland portions of the dunes numerous rather poorly developed Cladoniae and Cetraria aculeata were associated, while on the sides of “slacks” or “dune-pans” Collema pulposum, Cladonia sylvatica and several crustaceous lichens covered the soil. The wetter parts of the dunes were not found to be favourable to lichen growth.

Sandstede[1196] found on the sandy shores of Rügen, from the shore upwards: first a stretch of bare sand, then a few dune grasses with scattered scraps of Cladoniae, Peltigerae and Cetraria aculeata. Next in order sandbanks with Parmelia physodes, Cladonia sylvatica, Cl. alcicornis and Stereocaulon paschale. All these are species that occur on similar shores in the British Islands. Sandstede adds an extensive list of maritime species observed by him in Rügen.