IMCRA Regions: Central West Coast, Leeuwin-Naturaliste, WA South Coast.
Local Government Areas (LGAs): Albany, Rockingham.
Habit and structure. Thallus medium to dark brown, 5–20 cm long, irregularly alternately branched at intervals of (0.5–)1–3 cm, branches usually broadening from their base upwards, occasionally tapering near apices, 2–4(–7) mm broad, with the apical cell usually in a truncate apex or slight depression. Branches with occasional to numerous, irregular, surface proliferations, some developing into branchlets, with a terete base several cells in diameter. Attachment of thallus by numerous long, terete, fibres, 200–500 µm and 8–12 cells in diameter, issuing from the thallus surface near the base; epiphytic or epilithic. Cortical cells 15–20 µm across, L/B (1.5–)2–3(–4).
Reproduction. Tetrasporangia 100–180 µm in diameter, in more or less square, block-like patches on alternating sides of the thallus with the branch centrally concave to each patch and thus undulate; tetrasporangia sparsely to densely grouped in each patch. Oogonia unknown. Antheridial sori in similar concave, alternating patches to the tetrasporangia, sori irregular to slightly elongate in shape, 200–400 µm across, with individual antheridia 60–100 µm long and 15–30 µm in diameter.
Distribution. From Rottnest I., W. Aust., around southern Australia to Walkerville, Vic., and the N coast of Tas.
Habitat. R. radicans is a deep-water species, known largely from the drift but also collected from 7 to 38 m deep in S. Aust. waters.
[After Womersley, Mar. Benthic Fl. Southern Australia II: 190 (1987) as Dictyota prolifera]
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Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/