Dicranema revolutum (C.Agardh) J.Agardh

Scientific Description

Habit and structure. Thallus red-brown, fading to yellow-brown, cartilaginous, 2–5(–7) cm high, with rigid, terete, subdichotomous branches 400–600 µm in diameter, apices rounded, branched at intervals of mostly 2–10 mm. Holdfast crustose, extending around the host stems, with one to a few fronds; epiphytic on Amphibolis. Structure multiaxial with a narrow medullary core of slender elongate cells and a broad pseudoparenchymatous cortex of inner ovoid cells 20–40 µm in diameter and a small-celled outer cortex 2–3 cells thick, outer cells 2–3 µm in diameter. Rhodoplasts discoid to ribbon shaped, few per cell.

Reproduction. Sexual thalli monoecious; non-procarpic. Carpogonial branches 2-celled with long straight trichogynes, situated to one side of the branch apices. Auxiliary cells adjacent to carpogonia and fusing with them, then developing a fusion cell which produces gonimoblast filaments mainly thallus-inwardly with terminal obovoid carposporangia 30–65 µm long and 20–30 µm in diameter. Cystocarps swelling branches; pericarp consisting of the cortex, usually with an ostiole developing above the carposporophyte cavity opposite the auxiliary cell, by separation of the cortical cells. Spermatangia developed in sunken clusters from outer cortical cells which become buried in the cortex, with chains of 3–6 spermatangia 3–5 µm in diameter, released whole. Tetrasporangial nemathecia surrounding the apical 1 mm of branches, tetrasporangia basally attached to mid cortical cells, ovoid, 60–90 µm long and 25–35 µm in diameter, zonately divided.

Distribution. Shark Bay, W. Aust., to Walkerville, Vic., and Flinders I., Bass Str.

Habitat. D. revolutum is an obligate epiphyte on Amphibolis.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 322–324 (1994)]