The Botany of Iceland - 01.12.1930, Page 60

H. M0LHOLM HANSEN
50
and finally, 8—9 are the mo vegetation at a somewhat higher level
above the sea.
The mo vegetation is very rich in species, in 2.5 sq. m. there
occur on an average 35 species of phanerogams or c. 10 p. c. of all
Icelandic phanerogams. P’or the typical mo on Lýngdalsheiði the
density of species is 12—15. Tlie biological spectrum shows that
H forms the bulk of tlie vegetation, constituting 50—60 p. c. of all
the species noted. The Ch percentage is 25—30, the G percentage
15—2. Th occurs very sparingly. The proportion of the two spe-
cies groups A and E is as 1 to 1.
As far as the floristic composition is concerned it is difficult to
point out one or more species that are physiognomically dominant,
and in that respect the knoll formation is most conspicuous.
Of chamaephytes Salix herbacea and Empetrum nigrum are most
important, species such as Thymus serpyllum, Silene acaulis, and
Cerastium alpinum being less conspicuous. The other Salix species,
such as S. glauca, S. lanata, and S. phylicifolia are practically of no
consequence, and the same is the case with Vaccinium uliginosum
— this species occurs principally in mo which adjoins geiri, as
shown in table 11, 5. Calluna vulgaris and Arctostaphylos uva ursi
only occur in some few specimens in the mo round Lýngdalur;
further down, at the foot of Lýngdalsheiði, both species were phy-
siognomically predominant in the mo, whereas they were only found
in the geiri in Lýngdalur. Loiseleuria procumbens otily occurred
sporadically; higher up, at Thrasaborgir, it was considerably more
frequent. Of herbaceous plants Polygonum viviparum, Galium bo-
reale, G. Normanni and Thatictrum alpinum are most important, a
few other species occur more sporadicalljr, particularly Cardamine
pratensis.
It is, however, grasses or cyperaceous plants that dominate,
such as Festuca rubra, F. ovina, Agrostis canina, Carex rigida, Juncus
trifidus, Elyna Betlardi, Luzula spicata, further Deschampsia flexuosa,
Trisetum spicatum, Anthoxanthum odoratum, and Poa gtauca. Of
vascular cryptogams Selaginella selaginoides, Equisetum pratense, and
E. variegatum are most frequently met with, while Botrychium Lu-
naria and a few other Equisetum species occur now and again.
The typical mo on Lýngdalsheiði is thus characterised by a
long series of species, each species occurring with a mean frequency
characteristic of the species in question (mean F.-percentage) from
which value the individual occurrences deviate but little. In table 11,