Ptilocladia australis (Harv.) E.M.Woll.

Scientific Description

Habit and structure. Thallus light to dark red-brown, 3–8 cm high, slender, much branched irregularly, branches terete, with whorls of whorl-branchlets distinctly separated over most of the thallus leaving the axial cells exposed between them, in lower parts covering most of the axes, lower branches 0.7–1 mm in diameter, tapering to 150–360 µm near apices. Attachment by rhizoids from axial cells and basal cells of whorl-branchlets; mainly epiphytic on Posidonia and larger algae. Structure. Axes with short apical cells, enlarging within a few cells to 10–15 µm in diameter and L/D 1–1.5, and increasing to 150–300 µm in diameter and L/D 3–5 in mid and lower parts, often short (L/D about 1) near the base; axial cells mostly remaining ecorticate, older axes with slight rhizoidal cortication; lateral branches arising from basal cells of whorl-branchlets. Whorl-branchlets in whorls of 4, 120–270 µm long, outer parts curved upwards, branched several times, basal cells 15–25 µm in diameter and L/D 1.5–2, tapering to terminal cells 7–9 µm in diameter and L/D 1.5–2, often with a hair; pyriform gland cells occur on the whorl-branchlets. Cells uninucleate; rhodoplasts discoid to elongate in smaller cells, ribbon like and oriented lengthwise in axial cells.

Reproduction. Gametophytes dioecious. Procarps replacing whorl-branchlets, with a supporting cell bearing a curved 4-celled carpogonial branch, and with growth of the branch axis continuing with further procarps. Post-fertilization the auxiliary cell divides and the upper cell produces lateral lobes 150–300 µm across of ovoid carposporangia 25–35 µm in diameter, the carposporophyte being protected by adjacent whorl-branchlets. Spermatangia are cut off from terminal cells of whorl-branchlets, ovoid, 2–3 µm in diameter. Tetrasporangia occur on lower cells of whorl-branchlets, sessile, subspherical, 30–70 µm in diameter, tetrahedrally divided.

Distribution.Shark Bay, W. Aust., to Walkerville, Vic.

Habitat. P. australis is commonest as an epiphyte on Posidonia and some algae in sheltered waters.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 61–63 (1998)]