Beard’s Provinces: South-West Province.
IBRA Regions: Esperance Plains, Jarrah Forest, Swan Coastal Plain.
IBRA Subregions: Perth, Recherche, Southern Jarrah Forest.
IMCRA Regions: Abrolhos Islands, Central West Coast, Eyre, Kimberley, Leeuwin-Naturaliste, Spencer Gulf, St Vincent Gulf.
Local Government Areas (LGAs): Albany, Augusta Margaret River, Busselton, Cockburn, Cottesloe, Derby/west Kimberley, Esperance, Greater Geraldton, Rockingham.
Habit and structure. Thallus pink to medium red or red-brown, fading to grey-red, densely tufted, 2–4(–6) cm high. Fronds dichotomous every (2–)5–8(–22) intergenicula, complanate or branched in various planes. Intergenicula terete, 120–200(–250) µm in diameter below, tapering to 80–120 µm in diameter near the apices, (70–)100–200(–250) µm long, L/D 1–3. Propagules absent. Holdfast at first discoid, 0.5–4 mm in diameter, bearing several erect branches which may produce recurved tendrils 50–160 µm in diameter; in calm waters, secondary holdfasts form when branch tips contact host or other branches; epiphytic (on larger brown algae, especially Cystophora, and the seagrass Amphibolis) or occasionally epilithic and comprising turfs in the lower intertidal zone. Structure. Medullary cells in 1(–2) tiers per intergeniculum; hairs common in a ring around upper edge of intergeniculum. Genicula 60–120(–180) µm long (often longer than intergenicular medullary cells).
Reproduction. Gametangial thalli dioecious. Female conceptacles amphoroid, externally 250–400 µm long and 250–400 µm in diameter, internal diameter 150–240 µm, with a thick fusion cell; carposporangia subspherical, 40–65(–80) µm in diameter. Male conceptacles fusiform, externally 400–650(–800) µm long and 200–320(–400) µm in diameter, internally 140–250(–320) µm in diameter, pore canals 80–170 µm long. Tetrasporangial conceptacles amphoroid, externally 350–500(–550) µm long and (200–)250–450 µm in diameter, internal diameter 200–370 µm, mature tetrasporangia 120–240 µm long and 45–65(–90) µm in diameter.
Distribution. Geraldton, W. Aust., to Walkerville, Vic., and around Tas., N.S.W. New Zealand.
Habitat. J. micrarthrodia is common on larger brown algae, especially on species of Cystophora on rough-water coasts.
[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 299–303 (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/