Halarachnion ligulatum (Woodward) Kützing
The tetraporophyte is known as Cruoria rosea (P.L. Crouan
et H.M. Crouan) P.L. Crouan et H.M. Crouan, at least partly
Description: Gametophyte are thin, filmy to
subcartilaginous, deep brownish red, flattened fronds, 500 mm
long, simple to much-divided with very narrow segments, arising
from a small basal disc. Often marginally and superficially
proliferous. Tetrasporophyte is known as the Cruoria rosea-phase
and forms thin, rounded crusts on shells, stones and maerl
fragments in the subtidal (nn m).
Habitat: Gametophytes are annual (most obvious
in April-June) and occur on rock, stones, shells, and maerl in
spring and early summer in the shallow subtidal, although
isolated plants may occur to 32 m, widely distributed, frequent.
Tetrasporophytes occur on maerl, and reproduce by tetrasporangia
all year around.
Distribution: Widespread, mainly western in the
British Isles from the Shetlands to the Channel Islands. Europe:
the Mediterranean, Spain, France, Denmark, Helgoland, Denmark
and the Baltic. South to the Canary Islands and Morocco.
Similar species: Another annual,
Halymenia latifolia Kützing, is more delicate, is
usually elongated and tongue-like, occurs later in the year
(July-November) and is very rare on western and southern shores,
where it occurs exclusively on maerl.
Key characteristics: The gametophytes are filmy
and delicate, and lack veins or frilly margins. Situation
(shallow subtidal) and time of year (April-June) are helpful in
making an identification.
Link:
Algaebase
Species list
Red Bay, Co. Antrim, Northern Ireland. 18 m. 15 June 2006.
Calliblepharis ciliata
below and behind. Picture © Bernard Picton, Ulster Museum.
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