The Botany of Iceland - 01.12.1930, Qupperneq 113

STUDIKS ON THK VKGKTATION OF ÍCKI.AXI)
103
Of plants which are characteristic, that is to say, which either
occur here exclusively or occur here with the greatest F.-percentage,
or which are comparatively frequent on melar, we may mention
the following chamaephytes: Thijmus serpgllum, Cerastium alpinum,
Arahis petrœa, Minuartia verna, Arenaria ciliata, Saxifraga cœspitosa,
and S. oppositifolia, Drgas octopetala, Empetrum nigrum, Salix her-
hacea, and Silene acaulis. 01' hypogeophytes we mostly meet with
grasses and cyperaceous plants. Tlie following species occur: Poa
glauca, Fesluca ovina, Juncus trifidus, Luzula arcuata, and L. spicata,
further Polggonum viviparum. Of species found exclusively on melar
nnd thus characteristic of this type, we may mention Arabis petrcea,
Luzula arcuata, Saxifraga ctcspilosa and S. oppositifolia. Of thero-
phytes only Euphrasia latifolia occurs.
The Betula nana mo. Cf. fig. 18 and table 22 A, 7—11.
This type of vegetation, provisionally named after its dominant
chamaephyte, Betula nana, and referred to the mo on account of its
comparatively close carpet of vegetation, occurs especially in large
flat stretches among tracts of melar. The surface is not knolly as
in the typical mo, nor does solifluction occur in any appreciable
degree, as in melar. In small hollows in the Betula nana mo (the
level mo), we meet with the knoliy mo, which would seem to in-
dicate a comparatively low degree of moisture in the soil of the Betula
nana mo. Its distribution points to a snow-covering intermediate
between the two types melar and knolly mo.
The vegetation is continuous, a feature which renders the Betula
nana mo physiognomically very different frorn melar. The number
nnd density of species are, however, not very much higher than in
melar, the number of species being 32, the density 11.3, varying
from 10.4 to 13.0. In the biological spectrum Ch are still dominant,
even though the Ch percentage is reduced from 52 to 47. The re-
duction of the Ch percentage has resulted in an increase in the G
percentage frorn 9.9 to 15.2. The species group spectrum shows a
similar change; the A percentage has been reduced from 81 to 70,
the A 3 percentage from 55 to 43, wrhile, on the other hand, the A 2
percentage has risen. The increase of the E percentage falls prac-
tically only to E 4, which shows a percentage of 29 against 19 in the
melar vegetation. The E 3 group onlj' occurs with a percentage of 0.8.
The difference betw'een melar and the Betula nana mo is most
striking in a floristic respect, as even a hasty glance at table 22 A