Cystophora retorta (Mert.) J.Agardh

Scientific Description

Habit and structure. Thallus medium brown, 20–80(–120) cm long, openly branched in one plane. Holdfast discoid-conical, 0.5–1.5 cm across, with a single, terete, stipe; epilithic. Primary axes strongly compressed (W/T2–3), relatively straight, 2–5(–7) mm broad and 1–2 mm thick, alternately distichously branched from the face; secondary axes (2–)4–12 cm long (occasionally developing as main axes), 0.5–3 cm apart, usually not retroflex, leaving slight, stubby, residues, sometimes scalariform on secondary axes. Laterals 3–7 cm long, 1–5(–10) mm apart on axes, branched in one plane with ramuli alternate but soon becoming subdichotomous with broadly rounded axils; ultimate ramuli 1–5 cm long, 0.5–1 mm in diameter, terete or slightly compressed. Vesicles usually absent or rare, occasionally plentiful, replacing basal ramulus of a lateral, ovoid to ellipsoid and often asymmetric, petiolate, 5–14 mm long and 2–5(–9) in diameter, mutic (or apiculate when young).

Reproduction. Thalli monoecious. Receptacles mostly simple, (1–)2–5(–8) cm long and 1–2 mm thick, terete to slightly compressed, undulate to slightly torulose. Conceptacles normally bisexual, often separated by sterile tissue, with ostioles more or less in two rows, with simple paraphyses; oogonia sessile, ovoid, 80–110 µm long and 60–90 µm in diameter; antheridia sessile or on branched paraphyses, elongate-ovoid, 16–24 µm long and 8–12 µm in diameter.

Distribution. From Nickol Bay, W. Aust., to Wilsons Promontory, Vic., and around Tas.

Habitat. C. retorta is often a common species in larger pools and the upper sublittoral (to 21 m deep) with moderate water movement.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 392 (1987)]