IMCRA Regions: Central West Coast, Leeuwin-Naturaliste.
Local Government Areas (LGAs): Augusta-Margaret River, Irwin.
Habit and structure. Thallus erect, 1–3 cm high, subdichotomous, branches slightly compressed, 2–3 mm across near the base and tapering to about 1 mm in diameter near the rounded apices. Holdfast crustose, 1–4 mm across; epiphytic on Amphibolis. Structure multiaxial, with a filamentous medulla and a narrow, compact cortex, with the outer cortical cells bearing hyaline, thick-walled and terminally rounded hairs bent towards the branch apex.
Reproduction. Sexual thalli monoecious, with carpogonial and auxiliary cell branches scattered in the outer medulla. Carpogonial branches 9–12 cells long with the carpogonium sharply reflexed, cells 2 and 3 small and cells 4 and 5 larger and densely cytoplasmic, with post-fertilization fusion between the carpogonium and cell 4, resulting in an enlarged fusion cell producing several connecting filaments with basal pit-connections; lower cells of the carpogonial branch may bear single sterile cells laterally. Auxiliary cell branches 9–14 cells long, with the auxiliary cell usually fourth or fifth from the apex and slightly laterally displaced, with all the cells below and often above the auxiliary cell forming short lateral branches. Carposporophytes initially with 3–4 groups of gonimoblast cells, becoming globular (130–360 µm across) with most cells forming subspherical to ovoid carposporangia 10–13 µm in diameter, scattered in the outer medulla and not distending the cortex. Spermatangia cut off from the outer cortical cells. Tetrasporangia terminal on filaments of a crustose pad on Amphibolis stems, ovoid, 25–36 µm long and 9–12 µm in diameter, zonately divided.
Distribution. Port Denison, W. Aust., to Walkerville, Vic., always on lower stems of Amphibolis (A. antarctica and A. griffithii).
[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 227–228 (1994)]
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