The Botany of Iceland - 01.12.1945, Síða 109

THE VEGETATION OF CENTRAL ICELAND
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one place only, viz. on a mountain west of Hvannalindir, where, how-
ever, the vegetation should probably more correctly be termed Grim-
mia cushions than a closed heath. These cushions were mostly found
on a steep south-facing slope. A moss sample collected there contained
the following species: Grimmia hypnoides, G. canescens, Swartzia
montana, Hypnum revolutum, Encalypta alpina, Pohlia sp. Andraeaea
sp.; the samples contained only very few individuals of the last four
species, but the species of Grimmia were almost equally represented.
I assume that these mosses are, as a rule, found in the Grimmia heath.
On Snæfellsöræfi the Grimmia heath is fairly widely distributed
between c. 700 and 850 m altitude. The Grimmia heath is less pre-
dominant here than on Landmannaafrjettur, being mixed with other
mosses, and Cetraria, also, occupies a rather prominent place. It often
forms net-like growths in the moss heath, and the meshes contain
mossy cushions. On Síðumannaafrjettur the moss heath is found even
in localities in which we might expect to meet with shrub heath. In
these tracts, however, it attains its most extensive distribution in the
vast lava field resulting from the outbreak of the Laki in 1783; this
lava field is largely covered by Grimmia heath, which is very poor in
phanerogams. According to my view the Grimmia heath only occurs
in places with a humid climate and no noticeable sand-drift. More-
over it occurs principally where the snow-covering is thin. This appears
clearly from the lava field, for the Grimmia only grows on the lava
ridges and in places in which the snow cannot linger long. The de-
pressions in the lava between the ridges harbour a quite different moss
vegetation and are generally much richer in phanerogams than the
ridges. Although the Grimmia heath prefers a humid climate, it does
not thrive where the soil may accumulate or retain great moisture.
The Grimmia heath has been described by several botanists. H.
Jónsson (1895, p. 70 ff) records it from East Iceland, and in
addition from southern Iceland and Snæfellsnes. Stefánsson re-
cords it from Grímstunguheiði (1895, pp. 201-202). However, we are
hardly here concerned with the typical Grimmia heath, the surface
being very knolly and the soil damp, at any rate during the early
summer. One of the commonest phanerogams is Cassiope hypnoides.
Stefánsson further says that this “Grimmia-mó” should “be re-
garded as a transitional form between the heather mó and the ex-
tensive bog vegetation” (translated from the Danish) ; no doubt he
is perfectly right in this conception. A similar Grimmia mó was observed
by me near Snæfell. Molholm Hansen (1930, pp. 40-43) re-