The Botany of Iceland - 01.12.1912, Side 167

MARINE ALGAL VEGETATION
153
stretches of the coast. It is the only species of this community
which forms a large, continuous and almost pure association, at
any rate over considerable areas. The upper part of the association
is, however, generally mixed with Delesseria sinuosa, Ptilota, Odon-
tlialia, Rhodophyllis and others, and then these species often occur
in such abundance that the community acquires its usual mixed
character; that is, several species occur dominantly side by side,
though no single species can be said to predominate.
Among the remaining species of the community Rhodophyllis
dichotoma is often rather social. It is very common for Euthora
cristata lo occur intermingled, but to judge from the dredgings it
seems to have a scattered growth. Ptilota pectinata may be of fairly
social growth in E. Iceland. Detesseria sanguinea and Polysiphonia
urceolata occur also in this community, the first mentioned ap-
pearing to be most frequent while, in a few places, the latter lias
been found in abundance.
Of the species with a scatlered growth which belong to this
community may be mentioned: Lomentaria clavellosa (20—40 melres),
L. rosea (20—40) and Plocamium coccineum (20 metres), all in the
Vestmannaeyjar; and also Turnerella Pennyi and Omphalophyllum
ulvaceum in E. Ieeland.
In many places the under-vegelation of the community is formed
of crustaceous species of Lithothamnion.
Of the intermixed species, Desmarestia aculeata and D. viridis
are very frequent. In E. Iceland Chorda tomentosa has heen found
intermingled in this community. In addition, Laminariaceœ ol' scat-
tered growth such as Laminaria hyperhorea, L. digitata, L. saccharina,
Alaria esculenta, f. pinnata and Alaria Pylaii occur very frequently;
they are the outposts of the Laminariacetc-comníunity.
It has been previously mentioned that many of the members
of this community grow on Laminaria stems, and that in several
places the community forms, together with species of Desmarestia,
the second layer of the under-vegetation of the community of
Laminariaceœ.
The community grows both on somewhat exposed and also on
exposed coasts, and occurs both on a rocky and on a pebbly sub-
stratum, and even on sand.
The semi-littoral Polysiphonia urceolata-associat'ion has much in
common with this community.
Hosenvinge (63) and, following him, Börgesen (12) call this