Mychodea disticha Harv.

Scientific Description

Habit and structure. Thallus medium to dark red-brown, fading to grey-brown, drying cartilaginous, 20–45 cm high, erect, with moderately compressed axes 1–4 mm broad bearing distichous, usually crowded, compressed laterals from the margins, more-or-less at right angles, usually 1–4 cm long and 2–5 mm broad; older ones sometimes with short surface ramuli; laterals and ramuli with acute apices and bases usually slightly constricted. Holdfast discoid, 2–4 mm across, with one to a few axes; epiphytic on Amphibolis or larger algae, or epilithic. Structure uniaxial, usually with a distinct apical cell and a central axial filament in young branches but becoming indistinguishable below in the filamentous central medulla, an outer medulla of large cells and slender filaments, and a cortex of anticlinal filaments, outer cells elongate-ovoid to clavate, 2–4 µm in diameter. Rhodoplasts discoid to elongate, ribbon like in inner cells.

Reproduction. Sexual thalli monoecious; procarpic; polycarpogonial. Carpogonial branches 3-celled, 3–6 borne on enlarged inner cortical cells on both sides of ramuli, with the auxiliary cell producing gonimoblast filaments and clusters of ovoid carposporangia 10–15 µm in diameter within a filamentous matrix. Cystocarps (1–3) in the upper part of ramuli, swelling the branchlets on both sides but not deflecting them, with slight enveloping tissue, non-ostiolate. Spermatangial clusters scattered, sunken in the outer cortex, with initials producing 2–3 ovoid spermatangia 1.5–2 µm in diameter. Tetrasporangia scattered in the outer cortex, basally to laterally attached, ovoid, 40–60 µm long and 17–30 µm in diameter, zonately divided.

Distribution.Port Denison, W. Aust., to Walkerville, Vic., and around Tas.

Habitat. M. disticha is usually a deeper-water species on rough-water coasts. 

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 458–460 (1994)]