Sporochnus comosus C.Agardh

Scientific Description

Habit and structure. Thallus medium to dark brown, usually 10–40(–55) cm long, with one to a few percurrent axes bearing radially long primary laterals 2–20 mm apart, with numerous short, determinate, branchlets radially arranged, each with a tuft of assimilatory filaments; attachment by a rhizoidal holdfast 1–6(–14) mm across and 1–4(–6) mm long, usually epilithic. Growth apical, with a convex branch meristem surmounted by a tuft of slender trichothallic filaments 2–4(–9) mm long, each with a meristem (3–)5–8 cells above their base, (14–)18–25 mm in diameter above with cells L/B(2–)3–7. Fronds slender to moderately robust, terete, 1–2 mm in diameter in lower axes of more robust plants and 200–400 µm in slender plants, decreasing to 300–400 µm in diameter near apices of robust plants and 150–200 µm in slender plants, with the short determinate branchlets 1–5(–10) mm apart, 0.5–2(–3) mm long and 70–100 µm in diameter when sterile. Structure haplostichous and pseudo parenchymatous, with a medulla of elongate cells and a single-layered, smooth-surfaced, cortex of cells 8–12 µm across and L/B1–2 near apices, increasing to 4–6 below; older axes thickening by periclinal divisions of cortical cells.

Reproduction. Sporangial receptacles ovoid when young , becoming elongate-clavate and often curved in older, more robust, plants, always with a sterile branch base, 0.2–2(–6) mm long and 300–500(–700) µm in diameter. Paraphyses (80–)100–160 µm and 5–6 cells long, simple or once branched, with the terminal cell larger, subspherical to pyriform, (10–)16–22 µm in diameter, bearing lateral, clavate, unilocular sporangia 20–30 µm long and (6–)8–10 µm in diameter. Gametophyte unknown.

Distribution. From the Houtman Abrolhos, W. Aust., around southern Australia and Tas., to the Calliope River, Qld.

Habitat. On rough-water coasts, to 41 m deep (robust form) or in sheltered areas 1–10 m deep.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 280–282 (1987)]