Green marine subtidal alga, epilithic, to 60 cm tall; holdfast discoid; erect fronds spongy, subdichotomously branched; branches mostly terete, to 10 mm diam., becoming compressed and to 2cm broad near dichotomies.
Beard’s Provinces: South-West Province.
IBRA Regions: Jarrah Forest, Swan Coastal Plain.
IBRA Subregions: Perth, Southern Jarrah Forest.
IMCRA Regions: Central West Coast, Leeuwin-Naturaliste, Shark Bay.
Local Government Areas (LGAs): Augusta-Margaret River, Busselton, Cockburn, Cottesloe, Dandaragan, Fremantle, Irwin, Rockingham, Shark Bay.
Habit and structure. Thallus light to medium green, erect, subdichotomously to laterally branched, to 60 cm high, with branches terete and 3–10 mm in diameter but usually compressed (to 2 cm broad) at and near points of branching, branches moderately soft. Utricles cylindrical to clavate, (130–)175–500(–700) µm in diameter near apices, (450–)650–1800(–2500) µm long; apices broadly rounded, wall usually remaining thin, occasionally slightly thickened; hairs (or scars) occasional to numerous. Medullary filaments usually 40–75 µm in diameter, with plugs usually adjacent to utricle base.
Reproduction. Gametangia elongate-ovoid, usually tapering above, 70–160 µm in diameter, (230–)270–430 µm long, several per utricle and borne on a short protuberance from utricle.
Distribution. From Champion Bay, W. Aust., to Walkerville, Vic., and the N coast of Tas.
Habitat. C. duthieae is usually found on coasts of slight to moderate water movement but occasionally on rough-water coasts, from low tide level to 25 m deep.
[After Womersley, Mar. Benthic Fl. Southern Australia I: 235–236 (1984)]