Sargassum ilicifolium (Turner) C.Agardh

Scientific Description

Habit and structure. Thallus thick and bushy, to 2 m tall, with a crustose-scutellate or creeping holdfast to 18 mm diam. which is usually covered in epiphytes and sand; in some plants giving rise directly to small leaves. Stipe terete, smooth or with branch scars, to 10 mm tall, 1.0–2.5 mm diam. Primary branches smooth, terete or slightly compressed, 1.0–2.5 mm diam. Secondary branches radial, smooth, except when covered in branch scars, subterete, 0.5–2.0 mm diam. Primary leaves ovate, lanceolate or oblanceolate, 20–75 mm long, 6–22 mm wide; margins entire to serrate; apices obtuse, rarely acute. Secondary leaves arising in an alternate pattern on stem, often in pairs, ovate, spathulate or lanceolate, (5–) 10–59 mm long, 3–20 mm wide, medium to dark brown, with a dentate to almost entire margin; distal edge of leaf can be simple or divided into two, forming a cup shape; apices obtuse; midrib percurrent; base asymmetrical, cuneate; cryptostomata scattered, variable in size. Vesicles mostly spherical, some elongate or obovoid, smooth, 2–7 mm diam., each with a compressed to leaf-like stalk the same length as the vesicle or slightly shorter. Plants monoecious or dioecious. Receptacles simple or once-branched, in racemose or cymose inflorescences; male receptacles smooth, subterete, 2–9 mm long, 0.5–1.0 mm diam.; female receptacles spinous, compressed, 2.0–6.5 mm long, 1–2 mm diam.; monoecious receptacles subterete to compressed, with marginal spines, 3–12 mm long, 1.0–1.5 mm diam. Conceptacles mostly unisexual; oogonia 160–230 µm long, 130–160 µm wide; antheridia oval, stalked, 11–21 µm long, 7–13 µm wide.

Distribution. Pantropical from East Africa across the Indo-Pacific to Tonga. In Australia, known from Geraldton (W.A.) around northern Australia to southern Qld.

Habitat. Epilithic in the subtidal.

[After Dixon & Huisman, Algae of Australia: Mar. Benthic Algae of North-western Australia, 1. Green and Brown Algae 258-260(2015)]