Hypoglossum heterocystideum (J.Agardh) J.Agardh

Scientific Description

Habit and structure. Thallus pale grey-red to medium red, usually 3–6(–10) cm high, with one to several much branched main axes, usually becoming densely tufted, branching irregular. Mature blades (1–)2–5(–8) mmbroad, usually tapering gradually above to pointed apices (which become rounded when mature), margins entire and straight to convolute. Cortication usually slight, becoming moderate on lower midribs of larger plants. Marginal cells near apices occasionally fuse and develop outgrowing rhizoids (probably for attachment). Holdfast small, discoid; epiphytic on Posidonia. Structure. All second-order cells produce third-order rows with the cells becoming elongate apart from the marginal (and often 1 or 2 submarginal) isodiametric cells; the margin remains relatively linear. Cortication commences on older parts of lesser blades by rhizoidal filaments from the transverse pericentral cells, lying over the longitudinal margins of the pericentral cells and on older blades covering the pericentral cells and becoming several layers thick on older midribs of larger plants. Cells uninucleate when small, 2–4 nucleate when larger; rhodoplasts discoid, becoming chained.

Reproduction. Gametophytes dioecious. Procarps single or few per blade, with 2 sterile groups (one 2-celled and one 1-celled) and a 4-celled carpogonial branch. Carposporophytes much branched from the basal fusion cell, with terminal elongate-ovoid to slightly pyriform carposporangia 20–50 µm in diameter; maturing singly and sequentially, and arising also from subapical cells. Cystocarps maturing on medium to larger blades, subspherical, basally constricted, not urceolate, (0.5–)1–1.5 mm in diameter; pericarp relatively thin, 2 or 3 cells thick. Spermatangial sori rounded, elongate or irregular, on both sides of the midrib of linear blades, usually separated by sterile areas but becoming confluent, arising from cells of the lateral cell rows and occasionally from the lateral pericentral cells. Tetrasporangial sori rounded to elongate, on young blades with normal cell development. Tetrasporangia arise following production of cortical cells, first from the lateral pericentral cells (rarely from transverse pericentral cells) and later from adjacent cells of second- and third-order rows, occasionally (sometimes frequently) from corticating cells in older sori, usually producing a regular gradation of maturity, 50–100 µm in diameter.

Distribution.Port Denison, W. Aust., around southern Australia and Tas., to Port Stephens, N.S.W. and possibly to Brisbane and the southern Great Barrier Reef. N Papua New Guinea. Philippines.

Habitat. Usually in shallow water but extending to 22 m deep.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 45–48 (2003)]