- Reference
- Austral.J.Bot. 210 (1959)
- Conservation Code
- Not threatened
- Naturalised Status
- Native to Western Australia
- Name Status
- Current
Scientific Description
Habit and structure. Thallus medium to dark red-brown, often with a greyish iridescence, becoming rose-red to grey-red and decomposing rapidly, erect, 5–20 cm high, much branched with slender branches distinctly but slightly laterally compressed and without flanking cells in vegetative parts; axes 200–500(–900) µm broad, tapering to 30–40 µm broad near the apices. Attachment by rhizoids with multicellular haptera, arising from cortical cells; epiphytic, possibly epilithic. Structure. Apical cell hemispherical with axial cells cutting off 4 pericentral cells in alternating sequence, with slightly larger lateral pericentral cells; flanking cells absent in vegetative branches. Segments L/D 1–1.5 above, increasing to L/D 1.5–3 below; slight cortication by longitudinal rows of small elongate cells occurs, but no monosiphonous filaments occur. Branching endogenous, largely adaxial. Cells uninucleate, larger cells multinucleate; rhodoplasts discoid, chained in larger cells.
Reproduction. Carpogonial branches borne on the adaxial transverse pericentral cell, with the lateral pericentral cells of several adjacent segments bearing flanking cells. Carposporophytes with an elongate basal fusion cell and much branched gonimoblast with clavate terminal carposporangia 30–40 µm in diameter. Cystocarps sessile, ovoid; pericarp ostiolate, 2 cells thick, ecorticate, outer cells transversely elongate. Spermatangia unknown. Tetrasporangial stichidia apparently rare, formed from ends of lateral branches with the upper 8–12 segments bearing tetrasporangia. Typical flanking cells develop on fertile segments, remaining undivided, with tetrasporangia in 2 longitudinal rows cut off from the lateral pericentral cells. Adaxial and abaxial cover cells partly protect the tetrasporangia, with the flanking cells becoming elongate and curved; tetrasporangia 40–70 µm in diameter.
Distribution.Known from Fremantle, W. Aust., and from Torrens "Strait" (Outer Harbor) and American R. inlet and Penneshaw, Kangaroo I., S. Aust., and Port Phillip, Vic.
Habitat. M roeanum occurs in calm water situations.
[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 152 (2003)]