Furcellaria lumbricalis (Hudson) J.V. Lamouroux
Also known as Furcellaria fastigiata and as Black
Carrageen (English); Leaba Phortáin (Irish:
Crab's Bed).
Description: Cartilaginous, cylindrical, brownish-black
fronds, repeatedly dichotomously branched with narrow axils,
fastigiate, to 2 mm diam. and 300 mm long, with acute apices.
Attached by much-branched rhizoids. Multiaxial, medulla of
cylindrical cells interspersed with rhizoids, cortex of
irregular filaments, inner cells elliptical, outer cells narrow,
elongated, in radial rows. Reproductive structures are formed in
pods in winter (below), which are generally shed in spring with
apical growth resuming.
Habitat: On rocks, lower intertidal and shallow subtidal,
in pools and runnels, in open situations, often on sandy or
muddy shores, tolerating lowered salinities. Widely distributed,
common.
Distribution: Spitsbergen south to Spain.
Similar species:
Polyides rotundus is
similar in expternal appearance but has a discoid attachement
structure instead of a rhizoidal one. Furcellaria is
also brown if you hold it up against the light, whilst
Polyides is red in transmitted light.
Usage: A detached form was once collected in Denmark for
carrageenan (furcellaran) production but stocks are now
exhausted; all carrageenan produced in Denmark now comes from
foreign sources.
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