IMCRA Regions: Leeuwin-Naturaliste, Otway, WA South Coast.
Local Government Areas (LGAs): Cockburn, Esperance.
Habit and structure. Thallus medium to dark brown, very mucoid, much branched usually with relatively long laterals, 10–50 cm long and 1.5–4(–7) mm in diameter, with a small discoid holdfast 1–3 mm across, epilithic. Medulla becoming hollow, of more or less parallel, adhering, longitudinal, cylindrical filaments 25–45 µm in diameter with cells L/B (1–)1.5–6(–20) in the inner medulla, with few to moderately abundant hyphae and with slightly slenderer peripheral filaments. Subcortex slight, 30–50 µm broad and of 1–3 cells (branched if 2 or 3) at right angles to medullary cells, filaments 8–12 µm in diameter and cells L/B (2–)3–6, with the inner cells producing occasional hyphae. Cortical filaments arising singly or in groups from outer subcortical cells, or directly from peripheral medullary cells, simple, determinate, 200–400(–500) µm and 15–30 cells long when mature, curved to recurved above, with intercalary divisions; upper cells more or less moniliform, subspherical to ovoid, 10–14 µm in diameter and L/B 1–2(–2.5), lower cells cylindrical, 6–8 µm in diameter and L/B (2–)3–5. Phaeoplasts several per cell, discoid, each with a pyrenoid; physodes numerous. Phaeophycean hairs usually frequent, arising from outer subcortical cells, 8–12 µm in diameter.
Reproduction. Plurilocular sporangia produced from upper cells of curved cortical filaments by subdivisions on their upper side, 2–4 cells and 10–30 µm long and 6–10 µm in diameter. Unilocular sporangia borne on outer subcortical cells, ovoid to broadly clavate, usually sessile, (50–)60–80 µm long and 20–45 µm in diameter.
Distribution. From the Head of the Great Australian Bight, S. Aust., to Watsons Bay, Sydney, N.S.W. and around Tas.
Habitat. Usually in the lower eulittoral or uppermost sublittoral as a summer annual (October to February).
[After Womersley, Mar. Benthic Fl. Southern Australia II: 122–124 (1987)]
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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/