Alga Padina australis

Appearance

Thallus blade-like, solitary or in clusters, 10-15(-20) cm high, 2-8 cm broad, broadly flabellate, always split into lobes, yellowish-brown, lightly calcified. Lobes fan-shaped, flat with inrolled outer margins. Thallus distromatic through the whole blade, 80-115 μm thick near the base, 40-50 μm thick in the upper portion. Cells of the upper layer smaller than that of the lower one. Alternate zonation of narrow (1.5-2 mm) fertile glabrate band (with non-indusiate tetrasporangia) and the wider (2-3 mm) sterile band. Tetrasporangia obovate, (50-)110(-140) μm long and 70-90(-118) μm diam., in continuous groups or scattered in concentric lines distal to every hair band on the outer surface. Hair bands alternated on the upper and lower surfaces. Attachment by single stypose holdfast (consisting of 7 layers of cells). Growing on middle intertidal to subtidal rocks and dead corals exposed to moderate wave action.

Distribution

Tropics and subtropics of Atlantic, Indian and Pacific Oceans.

Habitat

It typically grows where there are sandy, clayey or silty sediments in pools beneath receding mudstone and sandstone cliffs. Other habitats include mangrove roots, rocks, pieces of shell, seagrass meadows and coral reefs on flats in the lower intertidal zone.