IMCRA Regions: Leeuwin-Naturaliste, WA South Coast.
Local Government Areas (LGAs): Albany, Busselton.
Habit and structure. Thallus medium red to red-brown, fading to grey-red, 2–5(–10) mm high, epiphytic on Cystophora spp. and Platythalia angustifolia. Fronds 3–10(–12) intergenicula long, complanately branched every one or two intergenicula. Intergenicula subterete below, compressed and ovate to cuneate above, increasing in size upwards, 400–1200 µm long, 200–600(–800) µm broad and 180–340 µm thick, 300–500 µm thick where conceptacles are present. Holdfasts discoid to pulvinate crusts, 200–1000 µm across, bearing up to 12 fronds each. Structure. Medullary cell tiers indistinct. Genicula (80–)100–160(–200) µm long.
Reproduction. Gametangial thalli dioecious; conceptacles deeply embedded and inconspicuous, terminal, or bearing simple branches. Female conceptacles internal diameter 100–200 µm when procarpic and 300–450 µm when carposporangial, with a thick fusion cell; carposporangia subspherical to ovoid, 100–160 µm in diameter. Male conceptacles internally 130–360 µm in diameter and 350–560 µm high, canal about 100 µm long. Tetrasporangial conceptacles usually bearing two branches; internal diameter 300–450 µm; tetrasporangia 200–420 µm long and 100–160 µm in diameter.
Distribution. Yallingup, W. Aust., to Cape Patterson, Vic., and the NW coast (at least) of Tas.
Habitat. J. pusilla is common on species of Cystophora (especially C. subfarcinata) in shallow water on rough-water coasts in southern Australia.
[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 307–309 (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/