Metagoniolithon stelliferum (Lam.) Weber Bosse

Scientific Description

Habit and structure. Thallus medium red-brown but often bleached, 5–20(–30) cm high, with one to a few axes from a crustose holdfast, much branched from the genicula with clustered branches of varying lengths, ultimate branchlets of 1–2(–3) intergenicula, intergenicula 3–15(–20) mm long below and 0.5–1 mm in diameter, decreasing to (1–)2–4 mm long and 200–300(–400) µm in diameter above; apices of branches with a mucilaginous cap 25–30 µm thick. Holdfasts 1–3 mm across; epiphytic on Amphibolis directly or more often on other epiphytic crustose coralline algae, or on larger algae. Structure. Intergenicula of numerous medullary tiers 25–45 µm long, cells 6–14 µm in diameter with numerous lateral cell-fusions. Genicula relatively long, of untiered filaments. Apical cells separated, without epithallial cells. Cortex present on both intergenicula and genicula, below extending over the genicula as calcified collars, of short splaying filaments 7–10 µm in diameter, with short epithallial cells and often scattered hairs. Rhodoplasts discoid to elongate.

Reproduction. Conceptacles uniporate, borne on the surface of the intergenicula. Gametangial thalli dioecious. Female conceptacles 300–350 µm in external diameter, bearing 2-celled carpogonial filaments on the chamber floor; carposporophyte with a broad, thin, fusion cell with short marginal gonimoblast filaments developing ovoid, terminal carposporangia 20–30 µm in diameter. Male conceptacles 300–400 µm in external diameter, with spermatangia cut off from initials only on the chamber floor, ovoid, 1.5–3 µm in diameter. Tetrasporangial conceptacles prominent, conical, 300–420 µm in diameter, with 2–6 tetrasporangia at the periphery of the chamber, each 75–120 µm long and 30–65 µm in diameter, zonately divided.

Distribution.Yanchep, W. Aust., to Refuge Cove, E of Wilsons Promontory., Vic., and N Tas.

Habitat. M. stelliferum is common near low tide on coasts of moderate water movement, usually indirectly epiphytic on Amphibolis and occasionally on various larger algae or Heterozostera.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 320–321 (1996)]