Sargassum oligocystum Mont.

Scientific Description

Habit and structure. Thalli light to dark brown, 4–8 cm tall. Primary axes terete, 1–2 mm long; primary laterals strongly compressed, thin-edged, 3–5(–7) mm wide, distichously issuing coarse vertically aligned spinous leaves 2–3 cm long and 7–12 mm wide; bases symmetrical or slightly scalloped on the axillary side, most leaves truncated apparently by grazing, but intact leaves with obtuse spinous apices; apices of primary laterals broadly rounded, flattened, the leaf primordia produced alternately; midribs prominent proximally, fading well before the leaf tips. Cryptostomata prominent, mostly in a single staggered line on either side of the midrib, becoming irregularly scattered in oldest leaves. Vesicles absent; axillary structures infrequent, also vertically aligned, either dwarf leaflets or receptacles.

Reproduction. Receptacles flattened, without stalks, in flabellate or imbricate glomerulate cymes, marginally and apically spined, 2.5–3.6 mm long, 3.5–6.0 mm wide, the individual branches 1.2–2.3 mm wide and 600–750 µm thick, dioecious with monoecious conceptacles. Antheridia stalked, lining conceptacle sides and floors, the cavities to 200 µm deep; antheridia stalked and irregularly ovoid, mostly 14–16 µm long and 6–10 µm wide; eggs on the peripheral floors of cavities , 90–120 µm in diameter.

Distribution. Known from East Africa and South, South-east and East Asia, New Guinea, New Caledonia, Micronesia and the Solomon Islands. Also in tropical W. Aust., north-eastern Qld., Norfolk I. and Lord Howe I.