Dictyota gunniana (J. Agardh) Hornig, Schnetter & Prud'homme

Scientific Description

Habit and structure. Thallus medium to dark brown, 5–20(–25) cm long, with single or clustered axes from a matted base, regularly dichotomously branched below and much branched above dichotomously or becoming alternate, at intervals of 0.5–2(–6) cm, branches (0.5–)1–2(–5) mm broad, of fairly even width throughout or with branch ends becoming slightly spathulate (especially when proliferous), axils and apices rounded, with the apical cell not or slightly protruding; proliferations usually absent, occasionally abundant and mainly marginal. Holdfast rhizoidal; epilithic. Cortical cells 10–20 µm across, L/B 1–2(–3). Medulla near apices (1–)2 cells thick in centre of branches and (2–)3–4 cells thick near the margins, soon becoming 2–4 cells thick and usually 4 cells thick throughout older parts (in some specimens 5–7 cells thick); thickness in upper parts 140–200 µm centrally, 160–250 µm marginally, in older parts 300–500(–600) µm thick throughout. Hair tufts scattered, hairs 14–20 µm in diameter.

Reproduction. Tetrasporangia 100–160(–200) µm in diameter, scattered, usually sparse. Oogonial sori relatively small, round to ovate, 200–500 µm long and 200–300 µm across; oogonia 100–150 µm long and 60–100 µm in diameter. Antheridial sori elongate ovate, densely scattered, 400–900 µm long and 240–600 µm across; antheridia (50–)60–120 µm long and 20–40 µm in diameter.

Distribution.From Cliff Head, W. Aust., to Westernport Bay, Vic. and the N coast of Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 208–210 (1987) as Dilophus gunnianus]