Polysiphonia australiensis Womersley

Scientific Description

Habit and structure. Thallus dark red-brown, 4–10(–15) cm high, with one to several erect, percurrent axes from a clumped base, axes much branched above with fastigiate lateral branch systems usually not more than 1 cm long, often denuded below. Holdfast of tightly clumped rhizoids cut off from basal pericentral or cortical cells; epilithic or epiphytic on other algae. Structure. Lower axes 0.7–1.5 mm in diameter, heavily corticated, decreasing gradually to upper lightly corticated axes or branches 300–500 µm in diameter with segments L/D 0.3–0.8, within about 1 cm of branch apices; ecorticate branchlets 120–180 µm in diameter with segments L/D 0.7–1(–1.3), decreasing to 70–100 µm in diameter with segments L/D 0.3–0.7 near the apices; trichoblasts usually profuse, branches replacing trichoblasts and commonly cicatrigenous from older branches. Pericentral cells 4, usually elongate with L/D (1–)1.2–2(–2.5) in ecorticate parts except near apices, becoming corticate from the sides or corners of pericentral cells with corticating filaments developing longitudinally between the pericentral cells, soon spreading as a complete surface layer, becoming several cells thick on older axes; trichoblasts or scar cells present on every segment with a divergence of one quarter, relatively robust (basal cells 35–45 µm in diameter), 2–3(–4) times furcate. Rhodoplasts discoid, scattered.

Reproduction. Gametophytes dioecious. Carposporophytes with a small basal fusion cell and short gonimoblast bearing clavate terminal carposporangia 20–40 µm in diameter. Cystocarps stalked, ovoid, usually becoming urceolate with a pronounced neck, 200–350 µm in diameter and 300–400 µm long (excluding stalk); pericarp ostiolate, 2 cells thick, outer cells isodiametric to elongate, angular, with the ostiolar cells considerably enlarged. Spermatangial branches developing as one branch of a trichoblast, cylindrical to tapering, 150–300 µm long and 40–80 µm in diameter, with 1–2 sterile apical cells when mature. Tetrasporangia forming gently spiralling series in upper branchlets, usually extending below 1–3 branches, moderately distorting the segments and occupying 0.5–0.7 of the segment diameter when mature, subspherical, 40–60 µm in diameter.

Distribution.Rottnest I., W. Aust., to Curtis I., Bass Strait, Vic., and Three Hummock I, NW Tas.

Habitat. P. australiensis is a distinctive species, largely confined to the lower and mid eulittoral zones on sloping rock on rough-water coasts; occasionally it is epiphytic in the same habitats.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 197–199 (2003)]