Hypoglossum protendens (J.Agardh) J.Agardh

Scientific Description

Habit and structure. Thallus medium red, 5–20 cm high, with one to several main axes, usually widely spreading and much branched, mainly abaxially. Base of plant (holdfast and about 1 cm of upright stipe below the point of branching) probably perennial. Main blades becoming denuded below, leaving the heavily corticated midrib as an axis. Mature blades 3–5 mm broad throughout and often with upper curved ends; young blades narrower and tapering to a conical apex, becoming rounded when mature. Holdfast small, discoid; epilithic. Structure. Apical development with only the inner (3–)4–8 second-order cells producing third-order cell rows, the mature blades with up to 25 elongate (L/D about 5) cells between midrib and margin. Second- and third-order cell rows run obliquely (about 45° to midrib) across the blade. Margin of mature blade smooth to undulate, usually with 2 or 3 rows of small isodiametric marginal cells often cut off in pairs from larger submarginal cells; some of the small marginal cells extend to 2 or 3 cells long and project irregularly along the margin. Midrib becoming corticate on the lower half of the youngest blades by a central band of 6–10 longitudinal corticating filaments. Mature cells multinucleate; rhodoplasts discoid, becoming chained.

Reproduction. Gametophytes dioecious. Procarps not observed. Carposporophyte with carposporangia formed terminally and usually singly from the sequentially maturing cells of the gonimoblast, ovoid to pyriform, 50–100 µm in diameter. Cystocarps develop on either surface of the smaller blades, hemispherical when young, becoming massive, depressed globular and basally constricted, 1.2–3 mm across with virtually no neck and a small ostiole; pericarp 5 or 6 cells thick. Spermatangial sori covering the blades on either side of the midrib but with sterile areas of varying width along the margins and adjacent to midrib; sterile rows or patches also usually occur within the spermatangial area, running from midrib to margin, especially as sori develop. Tetrasporangial sori well defined, ovate to elongate and tapering, covering the midrib and up to half the marginal width, and with a coherent layer (becoming 2 or 3 cells thick) of cortical cells over the whole sorus. Cortical cells are present when tetrasporangia are initiated. Tetrasporangia first develop acropetally from the lateral pericentral cells, giving two distinct rows of sporangia, then spread laterally from other second- or third-order cells, also developed from both abaxial and adaxial residual transverse pericentral cells though only occasional tetrasporangia mature in these positions. Tetrasporangia do not originate from cortical cells and are usually regularly arranged in the sorus, but sometimes differ in their degree of maturity; tetrasporangia 100–180 µm in diameter.

Distribution.Fremantle and the Recherche Archipelago, W. Aust., to Port Phillip Heads, Vic.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 54–56 (2003)]