The Botany of Iceland - 01.12.1930, Page 94

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H. M0LHOLM HANSEN
of the knolls, especially on the side facing the sea (north), had
sometimes been deprived of its carpet of vegetation, exposing the
loose interior of the knoll to the desiccating and eroding action of
the wind. Hence large areas of the valley bottom have been trans-
formed into barren strelches of gravel covered with the melar ve-
gatation described above.
The number and density of species — especially the latter
are comparatively high in the mo both in comparison with the sur-
rounding vegetations and with the mo vegetation in other parts of
Iceland. The greatest density hitherto demonstrated, viz. 17.8, was
found on the mountain slopes of Yiðidalsfjall. H play a very pro-
minent part in the composition of the vegetation, while Ch have de-
creased. The G percentage has increased while the Th percentage
is unaltered, c. 3. The species group spectrum shows a change in
the same direction. The A and especially the A 3 species have de-
creased in quantity, whereas the E species, especially the lower sub-
groups, have increased.
Even if the chamaephytes are of subordinate importance in
respect of species and points, species such as Dryas octopetala,
Empetrum nigrum, Vaccinium uliginosum, and Thgmus serpyllum are
physiognomic. Of other dominant chamaephytes we may mention
Cerastium alpinum, Silene acaulis, Armeria vulgaris, and Salix herbacea.
Grasses and cyperaceous plants play a very prominent part, especially
Elgna Bellardi; further Luzula spicata, L. multiflora, Juncus trifidus,
Carex capillaris, C. rigida, and C. sparsiflora, Festuca ovina and F.
rubra, Poa gtauca and P. alpina, Agrostis canina, and Trisetum spicatum.
Of herbaceous plants we find especially Polggonum viviparum, and
Thalidrum alpinum, further Rumex acetosa, Tofieldia palustris, Ping-
vicula vulgaris, and Galium Normanni; of pteridophytes Selaginella
selaginoides and Equisetum spp., thus Equisetum arvense, E. pratense,
and E. variegatum. The Th are Euphrasia latifolia, Rhinanthus minor,
and Gentiana spp.
Some floristic differences may be shown to exist between the
different types of mo. In the low mo Deschampsia cœspitosa will
always be met with; even though the F.-percentage is not very high,
the species is physiognomically fairly predominant. Carex sparsiflora
is also more frequently met with in the low mo than at higher levels.
In the mo of the valley slopes the following species not found
at the bottom are met with. Equisetum variegatum, RhinanthllS
minor, Habenaria viridis, Parnassia palustris, and Bartschia alpina.