Habit and structure. Thallus light grey-red, (1–)2–6(–10) mm high, (10–)20–40 intergenicula long, slender; fronds branching every (3–)5–10(–20) intergenicula, open to fastigiate, mostly in one plane. Intergenicula terete to slightly compressed, (40–)60–100 µm in diameter, (100–)110–150(–165) µm long, L/D 1.2–2(–2.5). Holdfasts thin, crustose, 200–600 µm across, each bearing several erect branches; epiphytic on seagrasses or Myriodesma. Structure. Medullary cells in 1(–2) tiers per intergeniculum, each tier (30–)40–60 µm long; cortex one cell thick, organised in two tiers per intergeniculum, the distal of which cuts off apically small cells each of which produces a hair or hair initial. Genicula (35–)60–80 µm long.
Reproduction. Asexual by propagules borne laterally on intergenicula, propagules multicellular, compressed, more or less triangular and becoming bilobed, 120–200 µm long and 140–250 µm across the lobes when well developed, each attached by a pad 5–8 cells across, the lobes potentially developing branch buds which presumably may develop further. Gametangial thalli monoecious. Female conceptacles non-amphoroid, lying between the diverging arms of furcate intergenicula 200–280 µm long, branchlets containing other conceptacles sometimes growing from the developing arms; externally 280–360(–400) µm long and 180–240 µm in diameter, chamber diameter 150–200 µm when carposporangial, containing 3–6 subspherical to ovoid carposporangia each 40–100 µm in diameter. Male conceptacles terminal on short, simple, branches from the same basal crusts as branches bearing female conceptacles, externally 225–300(–430) µm long and 100–180 µm in diameter, chambers 70–110 µm in diameter and 425–590 µm high. Sporangial conceptacles between the diverging lobes of furcate intergenicula, the two (occasionally three) arms usually continuing as branchlets; externally 275–370 µm long and 230–270 µm in diameter (excluding arms), chambers 150–230 µm in diameter; each sporangium three-celled, consisting of a large two-nucleate cell and small basal and apical cells containing single nuclei, sporangia (140–)170–220 µm long and 50–100 µm in diameter.
Distribution. Albany, W. Aust., to Phillip I., Vic., on Posidonia, Heterozostera and Myriodesma.
[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 303–304 (1996)]
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Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/