Sargassum distichum Sond.

Scientific Description

Habit and structure. Thallus light to medium brown, 10–50 cm long, with a simple stipe 0.5–4 cm long, terete, 1–3 mm in diameter, with rounded branch residues, bearing apically and radially 1–3 primary branches. Holdfast discoid-conical, 4–12 mm across, with 1(–2) stipes; epilithic. Primary branches 10–50 cm long, axes slightly compressed below, terete to angular above, without spines, alternately distichously branched below with marginal laterals, radially branched above. Laterals (lower) 2–5.5 cm long, 3–6 mm broad, simple, linear lanceolate, serrate, apices acute, costate to just below the apex, with prominent scattered cryptostomata, grading to upper laterals of similar form but 0.5–4(–5) cm long and 2–4 mm broad. Vesicles axillary, subspherical, 2–3(–4) mm in diameter, with a slender, terete to slightly compressed, petiole (occasionally serrate), mutic or with a terminal leaflet.

Reproduction. Thalli monoecious. Receptacles bisexual, simple or rarely branched, compressed, 2–5(–7) mm long and 1.5–3 mm broad, with a central, swollen, fertile region and winged, coarsely serrate, lateral margins, occasionally with triquetrous wings near the receptacle apex; occasional receptacles terminate in a leaflet, with scattered ostioles. Conceptacles normally unisexual; oogonia sessile, ovoid, 150–310 µm long and 110–250 µm in diameter, very few per conceptacle; antheridia sessile or on short, branched, paraphyses, ovoid, 16–24 µm long and 10–14 µm in diameter.

Distribution. From Quobba, W. Aust., around southern Australia to Port Phillip, Vic.

Habitat. S. distichum is essentially a deep water species.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 444–446 (1987)]