The Botany of Iceland - 01.12.1945, Qupperneq 111

THE VEGETATION OF CENTRAL ICELAND
453
Icelandic Grimmia heath have a particularly large number of phanero-
gamous species in common.
(Table XVII-XVIII A-B).
I have not been capable of distinguishing more than two associa-
tions within the Grimmia heath; I assume, however, that more associa-
tions would be found if it were subjected to a more accurate investiga-
tion.
i. Salix herbacea—Polygonum viviparum-Ass.
(Tab. XVII. A-B, 1-4, 6; XVIII, A-B, 5-6).
Salix herbacea and Polygonum viviparum are the dominant species
everywhere in this association, but in addition to these, other dominants
have bcen found in a few analyses. Thus Festuca rubra is very common
in XVII, 1-3, F. ovina in XVII, 4, Poa alpina in XVII, 1-2, and
Elyna Bellardi in XVII, 4. Hence these four analyses may be said to
represent a grassy variant of the association, but none of these species
are present in such great numbers that they might be termed character
species of the association. Analyses XVII, 1-3 were taken in the afore-
mentioned mountain near Hvannalindir, where the Grimmia heath is
mostly found as rather small cushions on the mountain sides at an
altitude of 850-950 m. The mountain sides are very steep, but I noticed
no difference in the formation owing to difference in exposure. These
analyses show the lowest number of species and the lowest geophyte
percentage of the Grimmia heath, while the H percentage is relatively
high. Analysis XVII, 4 is from the mountain Loðmundur, altitude 970
m, from the mountain plateau proper, where the Grimmia heath forms
a rather extensive growth. The H percentage is much lower here than
in the preceding analyses. Analysis XVII, 6 was taken on the moun-
tain Kýlingur at an altitude of c. 790 m. Only few gramineous plants
were found in this locality, whereas chamaephytes dominate, and Rho-
diola rosea is likewise very conspicuous physiognomically in spite of
its low degree of covering. The analysis was taken in a locality situated
between the localities of analyses XVII, 5 and 7. Here the terrain is
highest and most exposed to the wind, and the snow-covering is, no
doubt, thinnest. Analyses XVIII, 5-6 are both from Síðumannaafrjet-
tur. The A percentage is somewhat lower here than in the other
analyses, but otherwise there is nothing particularly noteworthy; both
analyses were made in a slopíng terrain, analysis 5 in the mountain