Mychodea carnosa Hook.f. & Harv.

Scientific Description

Habit and structure. Thallus medium to dark red-brown, 10–30(–40) cm high, much branched irregularly radially with long axes 3–4 mm in diameter and main branches, with progressively slenderer and shorter laterals, the branchlets usually tapering abruptly to a point and often basally constricted. Holdfast crustose, knobby, 2–5 mm across; epilithic or on solid substrata or epiphytic. Structure uniaxial with a prominent apical cell and each axial cell forming two periaxial cells and filaments, soon producing cross-connector cells and a filamentous central medulla with the axial filament indistinguishable, surrounded by the large-celled outer medulla (with abundant secondary pit-connections) derived from inner cells of the periaxial filaments; cortex small-celled, 2–4 cells thick, outer cells ovoid, 2–4 µm in diameter, forming rosettes around the subsurface cells. Rhodoplasts discoid, becoming ribbon like in inner cells.

Reproduction. Sexual thalli monoecious; procarpic; polycarpogonial. Carpogonial branches 3-celled, 2–6 borne on enlarged inner cortical (supporting) cells, directed outwards. Supporting cell becoming the auxiliary cell, producing gonimoblast initials laterally and inwardly, forming branched filaments of cells which ramify between surrounding vegetative cells with pit-connections to them, ultimately forming small groups of branched chains of ovoid carposporangia 8–15 µm in diameter within the matrix of sterile tissue. Cystocarps immersed but swelling the branchlets, usually subterminal, with slight filamentous enveloping tissue and a further developed outer cortex except for just outside the auxiliary cell where a cortical depression remains; ostiole absent. Spermatangia in scattered clusters in the outer cortex, with cortical cells producing a ring of 4–6 initials, each cutting off two elongate spermatangia 2–3 µm in diameter. Tetrasporangia scattered, transformed from mid cortical cells, originally bearing outer cortical cells and thus intercalary, ovoid, 28–35 µm long and 15–20 µm in diameter, zonately divided.

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

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 451–454 (1994)]