Caulocystis cephalornithos (Labill.) Aresch.

Scientific Description

Habit and structure. Thallus medium to dark brown, 20–60(–100) cm long, with a short stipe bearing 1–6 primary branches, each much branched with laterals of limited growth. Holdfast discoid, (0.5–)1–2 cm across; epilithic. Primary branches terete, 1–3(–4) mm in diameter, bearing irregularly radial and moderately densely arranged laterals 3–20 mm apart, giving the branch an elongate-conical shape, with occasional, relatively short, secondary branches from the lower branch axis, and scattered vesicles borne directly on the primary branch axis or on older laterals; branch axes becoming denuded basally, with residues 1–5(–10) mm long; vesicles on a pedicel 5–10 mm long, elongate-ovoid to fusiform, tapering to both ends, 3–10 mm long and 2–4(–5) mm in diameter, with an apical mucro or awn, or occasionally bearing a normal ramulus or receptacle. Lateral ramuli simple to much branched at intervals of 3–20 mm, usually 5–15 cm long, terete, (0.5–)1–1.5 mm in diameter, with prominent cryptostomata. Growth from a single, three-sided, apical cell in an apical depression. Structure of a central, compact medulla of elongate cells with few hyphae, and a cortex of larger, isodiametric cells decreasing outwardly to the surface meristoderm.

Reproduction. Thallus monoecious. Receptacles developed from upper ends of ramuli, usually simple, terete, smooth, 2–10(–15) mm long and 1–2 mm in diameter, with scattered ostioles. Conceptacles numerous, bisexual, basal columella slight to conspicuous, with some phaeophycean hairs and paraphyses; oogonia sessile, ovoid, 60–130 µm long and 40–80 µm in diameter; antheridia sessile or on branched paraphyses, elongate-ovoid, 20–30 µm long and 6–10 µm in diameter.

Distribution.From Cape Naturaliste, W. Aust., around south-eastern Australia and Tas., to Bondi, N.S.W.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 360 (1987)]