Habit and structure. Thallus grass-green, lighter above, usually epilithic, sometimes epiphytic (e.g. on Posidonia), 10–30(–40) cm high and across, usually with a single frond from the holdfast, plane to irregularly divided or lacerate above, often perforate; intact margin in some places with slight to prominent microscopic, multicellular spines, occasionally almost entire, surface smooth. Cells in surface view in rows in both directions, more irregular below, isodiametric to slightly elongate, (8–)12–18(–25) µm across in both upper and lower parts, with 1–2 pyrenoids. Thallus 35–55 µm thick in upper parts with cells in transection rounded to ovoid and 12–18 µm high; 80–100 µm thick in mid parts with cells L/B 2–3, 25–35(–40) µm high, and usually tapering from their base (centrally in thallus) to their outer end; thallus just above rhizoidal region 100–200 µm thick, 120–200 µm thick near the base with cells L/B 2.5–4(–5) and 40–50 µm long, and tapering outwardly, and with a central mass of dense rhizoids.
Reproduction. Isomorphic with the sporophyte producing quadriflagellate zoo(meio)spores and the gametophytes unisexual with biflagellate anisogametes.
Distribution. Widely distributed in temperate (especially warm) seas.
[After Womersley, Mar. Benthic Fl. Southern Australia I: 142–144 (1984) as Ulva rigida]
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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/