Dictyota fastigiata Sond.

Scientific Description

Habit and structure. Thallus medium to dark brown, (5–)10–30 cm long, regularly dichotomously branched at intervals of (1–)2–8 cm, branches (2–)3–7 mm broad, linear, sometimes faintly zoned, axils acute to rounded, apices rounded with the apical cell not or only slightly protruding; proliferations absent except following damage. Holdfast rhizoidal; epilithic. Cortical cells 12–20 µm across, L/B 1–2. Medulla near apices and sometimes in older parts 2 cells thick centrally, older parts normally 4 cells thick, 4(–6) cells thick near the margins; thickness centrally 200–300(–400) µm,marginally (300–)400–500 µm thick. Hair tufts scattered, hairs 12–18 µm in diameter.

Reproduction. Tetrasporangia 120–180(–200) µm in diameter, scattered over the branches. Oogonial sori scattered, round to ovate, 120–240 µmlong and 100–160 µm across; oogonia 60–100 µm long and 25–50 µm in diameter. Antheridial sori scattered, irregularly ovate to elongate, 300–1000(–2000) µm long and 200–300(–500) µm across; antheridia 50–80 µmlong and 20–25 µm in diameter.

Distribution. From Geraldton, W. Aust., to Walkerville, Vic.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 206–208 (1987) as Dilophus fastigiatus]