The Botany of Iceland - 01.12.1912, Side 151

MARINE ALGAL VEGETATION
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Delesseria alata, Acrosiphonia, Polysiphonia urceolata, Ptumaria elegans
and Rhodymenia pahnata occur. Porphyra umbilicalis occurs as an
epiphyte in the Vestmannaeyjar, and also Cystoclonium, Polysiphonia
urceolata and otliers.
The Gigartina-belt is very luxuriant in the Vestmannaeyjar and
at Öndverðarnes; it may be said to be, on the whole, luxuriant in
S. and SW. Iceland. As regards the relations between Gigartina and
Corallina, tlie following observation from the Vestmannaeyjar may
be recorded. At Brimsurð, on the south-east side of the inhabited
island, where the littoral zone consisted of large, although not par-
ticularly high boulders, these were entirely covered above by a
dense Gigartina-vegetation, while Corallina formed just as dense a
belt around tlrem below.
Chondrus crispus also grows socially in S. and SW. Iceland.
It is true that Chondreta of lesser extent occur usuallj' at or near
low-water mark, but nowhere does the species occur nearly as
luxuriantly as does Gigartina. The Chondrus-xegcAiú'um is most
luxuriant in the Vestmannaeyjar and at Eyrarbakki. Between the
skerries off the latter place, the broad-fronded form grew in abun-
dance, both above and a little below the limit of low-tide. In both
the places mentioned, which belong to S. Iceland, it grows in such
abundance that the vegetation might almost be termed an associa-
tion; in SW. Iceland on the other hand, it seems to occur more
sparsely, and the small Chondreta may then be considered to be-
long to the Gigartina-associaúon.
Ahnfeltietum. Ahnfeltia plicata grows socially in S. and SW.
Iceland and usually forms a narrow belt at and below tlie limit of
low-tide. The individuals are very frequentlv matted together by
the byssal threads of various small molluscs, and worms and quan-
tities of snails are found between the plants. In reality this vege-
tation is more nearly related to the Cora/Zi’na-association than lo
the Gigartina-association. This species grows also scattered among
Coraltina and Gigartina.
The intermingled species are only few in number, for example,
Ralfsia deusta which may occur abundantly in small depressions,
and Leathesia difformis which sometimes occurs in abundance as
an epiphyte. Almfdtia is most frequently decoloured ahove low-
water mark.
Chætomorpha Melagonium occurs rather frequently, grow-