Mychodea marginifera (Aresch.) Kraft

Scientific Description

Habit and structure. Thallus medium to dark red-brown, 5–15(–40) cm high, with clustered, flat, subdichotomous main branches 2–10(–20) mm broad, with marginal, ovate to elongate, basally constricted proliferous laterals 2–4(–10) mm broad, with rounded apices, and later with small surface proliferations. Holdfast crustose, 1–3(–5) mm across; epiphytic on Amphibolis and larger algae, or epilithic or on jetty piles. Structure uniaxial but with the apical cell and axial filament apparent only in very young (cultured) plants, older apices domed; mature thallus with an inner medulla of slender filaments, outer medulla of large cells, and a small-celled cortex, outer cells ovoid, 2–4 µm in diameter. Rhodoplasts discoid, becoming ribbon shaped in inner cells.

Reproduction. Sexual thalli monoecious; procarpic; polycarpogonial. Carpogonial branches 3-celled, 2–4 borne on enlarged inner cortical cells, auxiliary cell producing gonimoblast filaments thallus-inwards and laterally, forming clusters of ovoid carposporangia 12–20 µm in diameter in the filamentous matrix. Cystocarps (1–4) embedded within the rounded tips of main branches, 0.8–1.5 µm across; enveloping tissue slight, cortex breaking down outside the persistent auxiliary cell for release of carpospores. Spermatangial clusters scattered, sunken in outer cortex of main branches, with several initials each bearing two elongate-ovoid spermatangia 2–3 µm in diameter. Tetrasporangia scattered, sometimes in patches, on both surfaces of branches; laterally attached in the outer cortex, ovoid, 36–50 µm long and 15–20 µm in diameter, zonately divided.

Distribution.Port Denison, W. Aust., to Gabo I., Vic., and E Tas.

Habitat. M. marginifera is a fairly common species, epiphytic (often on Amphibolis or Acrocarpia) or on solid substrates, on rough-water coasts, from low tide level to 11 m deep.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 466–468 (1994)]