Mychodea aciculare (J.Agardh) Kraft

Scientific Description

Habit and structure. Thallus medium to dark red-brown, firm, 10–20(–40) cm high, irregularly alternately and radially branched, main branches subdichotomous, terete, laterals 2–10 mm apart, 0.5–2 mm in diameter below, 200–500µm in upper parts, with numerous scattered, often curved, spines 0.5–1 mm long. Most branches, to near the tips, are infested with the partly endophytic hydrozoan Plumularia flexuosa. Holdfast originally discoid, later attached by a mat of hydrozoan tubes and by tendril-like ends to some lower branches; epiphytic on Amphibolis and various larger algae, epizoic on tunicates and sponges, and on rock. Structure uniaxial, with a persistent axial filament in the filamentous inner medulla, a large-celled outer medulla with few filaments, and a cortex of filaments of ovoid cells, the outer ones 4–8 µm in diameter. Rhodoplasts discoid to elongate, ribbon like in inner cells.

Reproduction. Sexual thalli monoecious; procarpic; polycarpogonial. Carpogonial branches 3-celled, 2–6 borne on inner cortical cells, with the auxiliary cell producing gonimoblast initials mainly thallus-inwards, then forming rows and clusters of ovoid carposporangia 10–15 µm in diameter within the filamentous matrix. Cystocarps developing in the base of the short spines, subspherical, 0.5–1 mm in diameter, with a prominent spine apex; enveloping tissue slight, cortex normal. Spermatangial clusters scattered, sunken in the cortex, with the initials producing 2–3 ovoid spermatangia 2–4 µm in diameter. Tetrasporangia scattered in the outer cortex, more or less basally attached, ovoid, 25–35 µm long and 15–20 µm in diameter, zonately divided.

Distribution. Cape Riche, W. Aust., to Walkerville, Vic., and around Tas.

Habitat. M. aciculare is a common species, from just subtidal to 24 m deep, in moderately sheltered localities. It grows on rocks, wooden pilings, and more rarely as an epiphyte or epizoic.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 462–464 (1994)]