The Botany of Iceland - 01.12.1930, Síða 72

62
H. M0LHOLM HANSEN
species in the three formations; if compared with table 11, it will
further show the agreement between the mo at Björk and that of
Lýngdalur.
The Elyna Mo. Table 14 A, 1—4. The dominant liere is Elijna
Bellardi. It occurs especially at the top of the knolls and with
its brown, tufted stems it contributes markedly to the peculiar
physiognomy of the vegetation. Other characteristic plants are
Silene acaulis, Cerastium alpinum, Trisetum spicatum, and Poa glauca.
These species attain their finest development here even though they
are also found in the otlier formations. P'urther it is characteristic
of the Elyna mo that a number of species otherwise always present
in the mo are rare or absent liere, viz. Vaccinim uliginosum, Calluna
vulgaris, Arctostaphylos uva ursi, Deschampsia flexuosa, Galium boreale,
and Luzuta multiflora. AIl these plants are southern species.
Tlie Arctostaphylos mo. Table 14 A, 5—7. Physiognomically
characteristic of this formalion are above all Arctostaphylos uva ursi,
Calluna vulgaris, and Vaccininm uliginosum; further there occur Des-
champsia flexuosa, Galium boreale, Luzu lamultiflora, and Anthoxanthum
odoratum. On the olher hand, Elyna Bellardi, Selaginella selaginoides,
Silene acaulis, Cerastium alpinum, Trisetum spicatum, and Poa glauca
are not dominant, a feature hy which this formation differs from
the Elyna mo. The difference between the two mo formations thus
consists in the fact that the Elyna mo has many arctic but conr-
paratively few southern species in contrast to the Arctostaphylos
mo in which the southern species are dominant. This difference is
decidedly due to the difference in the snow-covering. From both for-
mations the species requiring moisture, which occur in the Empetrum
mo, are absent.
The Calluna-Empetrum Mo. As inentioned above, this for-
mation occurs as a narrow border between the Arctostaphylos mo
and the jaðar, and it is particularly well developed where the ground
is slightly inclined. The most striking difference between this and
the above-mentioned formation is the absence of Arctostaphylos
uva ursi. Owing to the immediate vicinity of the jaðar some of
the plants characteristic of that formation are met with, though
sporadically, thus Carex sparsiflora, Cardamine pratensis, Deschampsia
cæspilosa, Taraxacum officinale, Agroslis tennis, Equisetum arvense,
Viola palustris, Salix lanata, and S. phylicifolia.