Sargassum swartzii C.Agardh

Scientific Description

Habit and structure. Thallus medium brown, to 60 cm tall, with a smooth compressed primary axis 1.5–2.0 mm wide. Primary branches smooth, flat, 2–5 mm wide, with sharp edges. Secondary branches smooth, compressed, 0.5–1.5 mm wide. Lower laterals lanceolate, variable in size, similar to upper laterals in some specimens or conspicuously larger, then 4–6 cm long, 6–10 mm wide; upper laterals becoming linear, serrate to dentate; apices acute; bases cuneate, subsymmetrical, 9–44 mm long, 1.5–8.0 mm wide. Vesicles ellipsoidal to subellipsoidal, smooth or with scattered cryptostomata, occasionally with a short mucro, (1.25–) 2.00–6.00 mm diam.; stalk narrow, compressed, usually shorter than the vesicle. Receptacles monoecious, arranged in cymes or short subracemose clusters, 1–3 times divided, verrucose, terete to subterete, bearing numerous spines and irregular branches, (0.75–) 1.00–3.00 mm long, 0.30–0.75 mm diam. Conceptacles monoecious; oogonia round to egg-shaped; 90–220 µm long, 73–210 µm wide; antheridia stalked, 16–27 µm long, 9.0–13.5 µm wide.

Distribution. Widespread in the tropical Indo-Pacific. Known from W.A. north of Coral Bay, and also from Qld.

Habitat. Epilithic in the subtidal.

[After Dixon & Huisman, Algae of Australia: Mar. Benthic Algae of North-western Australia, 1. Green and Brown Algae 257-258(2015)]