Martensia australis Harv.

Scientific Description

Habit and structure. Thallus medium to dark red-brown (the net usually darker than the lower membrane), 5–20 cm high, foliose with a frequently divided frond 10–25 cm broad, borne on a single stipe usually 1–2.5 cm long and 1–2 mm in diameter; lower solid membrane 2–8 cm high and broad, mostly 150–200 µm thick, entire or lacerate or subdivided, with the upper mesh (1–)5–15 cm high and as much or more across, radial and tangential membranes orientated at right-angles to the blades, mostly monostromatic, perforations elongate-rectangular, enlarging to 2–3 mm long and 200–400 µm wide; continuous marginal membrane (often lost) 1–3 mm across, with prominent, simple or branched, blunt spines 0.6–2(–3) mm long. Secondary nets usually absent. Holdfast discoid, 1–4 mm across; epilithic. Structure. Growth of marginal membrane from numerous marginal cells dividing irregularly, with submarginal cells dividing to form radial chains of cells which separate laterally and undergo extensive intercalary divisions to form the main radial segments of the net, becoming linked tangentially by lateral segments; this process continues extensively to form the relatively coarse mesh, with segments 500–800 µm and 14–18 cells broad. Lower membrane 200–400 µm and 4–6 cells thick, cell arrangement regular in section. Stipe becoming many cells thick, cells in tiers, equivalent. Mature cells multinucleate; rhodoplasts discoid, becoming chained.

Reproduction. Gametophytes dioecious. Procarps not observed. Carposporophytes with a basal pad of ovoid, darkly staining, cells below a basal rounded to erect fusion cell bearing a gonimoblast of several large, basal, clavate cells with branched filaments of progressively smaller cells and ovoid terminal carposporangia 15–35 µm in diameter. Cystocarps on the radial segments, globose, 1–1.5 mm across; pericarp ostiolate, 200–450 µm and 5–15 cells thick, cells in tiers. Spermatangial sori rounded to elongate, on the mesh segments, with small cortical initials each cutting off several elongate spermatangia. Tetrasporangial sori rounded, scattered on the mesh segments or on the lower solid membrane, 200–400 µm across, each with several tetrasporangia developed from primary cells and covered on each side by a layer of smaller cortical cells, tetrasporangia subspherical, 50–80 µm in diameter.

Distribution.Houtman Abrolhos (?) and Rottnest I., W. Aust., to Coffs Harbour, N.S.W. and N Tas. N Papua New Guinea. Philippines. Japan and China.

Habitat. M. australis is a deep-water species, usually in shade when in shallow depths.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 95–98 (2003)]