Himanthalia elongata (Linnaeus) S.F. Gray Common names: Ríseach
(Irish); Thongweed, Buttonweed, Sea Spaghetti (English).
Description: Thallus consisting of a button-shaped vegetative
thallus to 30 mm wide and 25 mm high, and a long, narrow, strap-
like, sparingly branched, light yellow-brown reproductive
receptacle to 2 m in length and up to 10 mm in width, on which
the conceptacles are borne. Buttons, initially club-shaped (top)
but later mushroom-like (above), develop from zygotes in late
summer, mature in winter, and begin to form the reproductive
receptacles in January/February. Some 4-6 dichotomies are
produced at this stage, and the fronds then elongate and thicken
without developing any further branches, and become
reproductively mature in July-September. Habitat: on gently
sloping rocks at MLWN, particularly on semi-wave-exposed shore
(below), on which they may form a distinct zone at low water.
Sparse populations sometimes develop in sheltered lagoons and
the plants are more yellow and less flattened.