Sargassum marginatum (C.Agardh) J.Agardh

Scientific Description

Habit and structure. Thallus medium to dark brown, bushy and erect, to 23 cm tall, with a discoid holdfast to 9 mm diam. Primary branches growing directly from the holdfast, 4–7, smooth, compressed, to 20 cm long, 1.5–2.5 mm wide. Secondary branches alternate, compressed or subterete, to 15 cm long and 1 mm wide. Primary laterals ovate to lanceolate, serrate, with rounded apices and a cuneate base, usually asymmetrical, 12–55 mm long, 9–13 mm wide; midrib fading between half-way to a few millimetres below the apex; stalk flat, 1.5–2.0 mm wide, merging into the leaf blade; cryptostomata small, scattered. Secondary leaves distinctly obovate, with rounded apices and asymmetrical bases, serrate, 8–20 mm long, 5–8 mm wide; midrib fading well before apices; cryptostomata small, scattered. Vesicles spherical, smooth, mutic, 1–3 mm diam. Plants monoecious. Receptacles clustered in stalked inflorescences associated with vesicles or (rarely) a leaf, clavate to compressed, spiny and occasionally winged, 2–6 mm long.

Distribution. Known from the Kimberley region, W.A., and Great Keppel Island, Qld; also in India, Sri Lanka, Indonesia and probably also Vanuatu and the Solomon Islands

Habitat. Epilithic in the subtidal.

[After Dixon & Huisman, Algae of Australia: Mar. Benthic Algae of North-western Australia, 1. Green and Brown Algae 262 (2015)]