Sargassum muticum (Yendo) Fensholt
Description: Thallus bushy, elongated,
yellowish-tawny to dark brown, generally to 4 m long (plants to
16 m have been reported from Brittany, but this is exceptional);
tough, cylindrical, repeatedly alternately pinnately branched to
the third or fourth order (below, left); whorls of distinctly
flattened sculpted leaves at the base (resembling the leaves of
Holly); with characteristic rounded-elliptical air bladders
(above and below, right) formed terminally. Reproductive
receptacles (below, right) formed in the axils of spiny leaves;
spectacularly fecund. Basal holdfast penetrating and conical,
persisting for several years. Reproductive plants detach easily,
and continue to reproduce while drifting, and spreading the
reproductive zygotes that develop on the surfaces of the
receptacles with the efficiency of a carpet-bombing aircraft.
Habitat: throughout the intertidal in pools
(below in June competing with
Bifurcaria bifurcataon the west coast of Ireland), but largest and commonest at low
water. Rarely growing below 5 m.
Distribution: widely distributed in S and W
Britain and throughout Ireland; also adventive in France, Spain
and Portugal; and the western Mediterranean. Alaska south to
Mexico. Native to Japan, China and Korea.
Key characteristics: Terminal air bladders
(below); receptacles in the axils of spiny leaves. Not to be
confused with
Gongolaria baccata
(air bladders in an intercalary position),
Gongolaria nodicaulis
(solid tophules at the bases of branches),
Halidrys siliquosa
(branched in one plane and with compartmented air bladders in
the shape of a seed pod).
Note: this is an introduced species from the
western Pacific, now widely distributed on the Pacific coast of
N America (Alaska to Mexico), the NE Atlantic and the
Mediterranean. First reported from the Isle of Wight on the S
coast of England in 1973, it was first found in NE Ireland in
the early 1990s, and is likely to have been spread initially by
shellfish movements. It's marginal spread from initial sites of
infection is facilitated by its extraordinary fecundity and its
ability to reproduce whilst floating.
Identification guide for selected marine non-native species (National Museum Wales). (Download free PDF, about 3.5 Mb).
Species list
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