Rhodymenia leptophylla J.Agardh

Scientific Description

Habit and structure. Thallus medium to dark red-brown, fading to grey-red, 4–10(–30) cm high, with numerous clumped fronds from slender entangled stolons, fronds flat, complanately branched, simple to furcately or palmately branched above with long stipes, branches 2–5 mm broad, usually broadest above, with no or few marginal proliferations, apices rounded when young, tapering in branched apices and often extending as long, subterete, prolongations 10–60 mm long; thallus 300–500(–800) µm thick; stolons and stipes slender, terete, 5–20(–60) mm long and 300–1000 µm in diameter, grading upwards to the flat fronds. Holdfasts small digitate pads on the stolons; epilithic. Structure multiaxial, developing a cortex 2–3 cells broad, outer cells ovoid and 2–4 µm in diameter, grading to the medulla 4–8 cells broad, cells rather laxly arranged, ovoid, 30–100 µm in diameter; stipe medulla 300–500 µm and 12–16 cells broad. Rhodoplasts discoid.

Reproduction. Gametangial thalli probably dioecious. Carpogonial and auxiliary cell branches not observed. Carposporophytes 250–500 µm across, with branched basal fusion cells bearing a dense mass of ovoid carposporangia 10–15 µm in diameter. Basal nutritive tissue slight, erect filaments absent. Cystocarps on the blade surfaces, often clustered, sessile, not or slightly basally constricted, slightly conical or beaked, 600–850 µm across, pericarp 100–150(–300) µm and 8–2(–25) cells thick (thicker around ostiole), inner cells irregularly placed and the outer cells in anticlinal rows of 3–5, ostiole usually depressed. Spermatangia not observed. Tetrasporangia in sori near branchlet ends, probably intercalary, the cortex slightly thickened with elongate outer cells and some additional small outer cells; tetrasporangia ovoid to elongate, 20–30(–40) µm long and 10–15 µm in diameter, decussately divided.

Distribution.New Zealand; N.S.W.; Qld. In southern Australia, from West I., S. Aust., to Westernport Bay, Vic., and around Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 73 (1996)]