The Botany of Iceland - 01.12.1914, Page 143
PHVSICAL GEOGRAPHY
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and S. annuum. As the environment of the ridges differs greatly —
sometimes bogs, sometimes dry grassland, sometimes heather —
the vegetation on the ridges also ditTers somewhat in the different
districts owing to immigration from these plant-associations. Mosses
Fig. 30. Dryas octopetala (Vallanes; June 26. 1909).
(Phot. A. Hesselbo.)
are few in number, but there is often an abundance of crustaceous
lichens, chiefly various species of Lecideas and Lecanoras, which often
impart a strongly variegated appearance to the rocky boulders.
River gravel has one characteristic plant all throughout Ice-
land, viz. Chamœnerium latifolium, the splendid, purple flowers of
which occur in large patches upon gravel-tongues between branching
rivers, and can be seen from a distance. Besides plants common
to gravelly flats several willows often occur here, viz. Salix glauca,
S. lanata and S. phylicifolia, and also Saxifragaceœ, Galium verum,
G. silvestris, and others. Clayey flats with a denser vegetation and
a soil rich in humus frequently occur at the outer edges of gravelly