Rhodopeltis australis (Harv.) Harv.

Scientific Description

Habit and structure. Thallus dark red-brown, fading to yellow-grey, 5–12 cm high and in spread, developing a terete to compressed, uncalcified stalk 1–3 mm in diameter, 1–7 cm long, knobby with branch remnants, bearing branches of 3–8 flat, ovate-elongate, heavily calcified segments, each bearing 2–4 branches terminally, separated by short, uncalcified nodes 0.5–1 mm in diameter; segments brittle, when mature 10–20(–25) mm long, (3–)4–8 mm broad and 200–600 µmthick, decreasing in size near branch apices; segments with an apical and basal indentation adjacent to nodes and usually with two longitudinal lines corresponding to the thinner marginal cortical regions. Holdfast discoid-conical, 2–10 mm across; epilithic. Structure multiaxial, with a dense filamentous medulla and a cortex of subspherical cells, the inner 40–50 µmin diameter, decreasing to the outer 3–4 µm in diameter; innermost cortical cells often stellate. Calcification (aragonite) in the cell walls throughout the cortex, not the medulla, with numerous large starch grains in cortical cells.

Reproduction. Reproductive organs in uncalcified, ovate nemathecia on both sides of thallus segments. Sexual thalli dioecious. Female nemathecia 160–200 µm thick, with dense paraphyses 12–15 cells long, lower cells elongate, 2-3 µm in diameter, upper cells ovoid, broadening to 4–6 µm in diameter. Carpogonial branches 6–8 cells long, cells 6–10 µm in diameter, L/D 1–2. Auxiliary cells apparently intercalary in filaments similar to carpogonial branches. Gonimoblast filaments branched, carposporophytes ovoid to elongate or lobed, 150–200 µmlong and 60–100 µm in diameter, developing densely massed carposporangia, carposporangia more or less isodiametric, 6–10 µm in diameter. Male nemathecia 80–120 µm thick with slender multicellular paraphyses branching laterally to form tufts of ovoid spermatangia each 1–2 µm in diameter. Tetrasporangial nemathecia shallow, 30–40 µm thick, with short, unicellular paraphyses 15–20 µm long and 3–5 µm in diameter; tetrasporangia clavate to ovoid, 20–25 µm long and 8–10 µm in diameter, irregularly cruciately divided.

Distribution. Cottesloe and Rottnest I., W. Aust., to Point Roadknight, Vic.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 166–167 (1994)]