Sargassum paradoxum (Turner) Gaillon

Scientific Description

Habit and structure. Thallus medium to dark brown, to 50 cm tall; holdfast discoid-conical, smooth, to 25 mm wide, giving rise to 1–3 primary axes, terete with occasional scars to 14 mm long, 3.0–3.5 mm diam. Primary branches densely whorled, angular, triquetrous, 2.0–4.5 mm diam. Primary leaves retroflex, lanceolate, 60–150 mm long, 14–23 mm wide, bent back, slightly ruffled, with undulating curls, serrulate; apices obtuse; base symmetrical, narrowly cuneate with minute scattered cryptostomata. Secondary branches angular, triquetrous, whorled, 1.5–2.5 mm diam. Secondary leaves whorled, lanceolate, 12–26 mm long, 3–8 mm wide, serrulate; apices obtuse; base asymmetrical, cuneate. Vesicles spherical, 2.0–3.5 mm diam., with a short apical mucro to 2 mm long. Receptacles monoecious, solitary or in racemose clusters, verrucose, flattened, leaf-like, 4–11 mm long, 1.5–2.0 mm wide, 0.4–0.5 mm thick. Conceptacles unisexual; oogonia round or oval, 100–145 µm long, 82–118 µm wide; antheridia elongate, stalked or sessile, 15–20 µm long, 7–9 µm wide.

Distribution. Known from North West Cape, W.A. south to Westernport Bay, Vic. and around Tas.

Habitat. Epilithic in the subtidal.

[After Dixon & Huisman, Algae of Australia: Mar. Benthic Algae of North-western Australia, 1. Green and Brown Algae 253-254 (2015)]