Platythalia angustifolia Sond.

Scientific Description

Habit and structure. Thallus dark brown, 20–80 cm long, with several complanately branched axes from the holdfast. Holdfast discoid-conical, soon becoming irregularly stoloniferous, 1–3 cm across; epilithic. Axes compressed, alternately pinnately branched, slightly flexuous, becoming denuded and relatively straight below, (2–)3–4(–5) mm broad and (0.5–)1–2 mm thick, with laterals 0.5–1 cm apart. Laterals simple to alternately pinnate, 1.5–4 cm long and (1–)2–3(–4) mm broad, basally constricted, entire, linear to lanceolate, with a slight costa. Medulla of elongate cells with few hyphae, and a cortex of isodiametric cells with a surface phaeoplastic meristoderm.

Reproduction. Thalli dioecious. Receptacles developed from branches of upper laterals, simple or branched. (1–)2–4 cm long and (1–)1.5–3(–4) mm broad. Conceptacles in two rows with marginal or submarginal ostioles, unisexual; oogonia sessile, ovoid, 120–180 µm long and 60–100 µm in diameter, with simple paraphyses; antheridia sessile or on branched paraphyses, ovoid, 25–30 µm long and 10–15 µm in diameter.

Distribution. From Flat Rocks, 40 km S of Geraldton, to Cape Riche, W. Aust.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 404–406 (1987)]