Padina australis Hauck

Scientific Description

Habit and structure. Thalli either erect and dissected into basally constricted flabellate lobes from a fibrous holdfast and a short stupose stalk, or ± horizontally spreading, sessile, frequently overlapping and broad to the base. Fronds to 11 cm long and 10.5 cm wide, broadly lobed to deeply incised and narrowly linear, lightly and mostly ventrally calcified, pale to dark brown. Apical margins circinnately coiled, unravelling into a planar 2-layered frond 90–120 µmthick. Cells of dorsal and ventral layers ± uniform in size, or the ventral layer cells smaller (25–60 µmlong, 24–27 µmwide and 33–45 µmtall) than those of the dorsal layer (40–87 µmlong, 20–25 µmwide and 50–72 µmtall).

Reproduction. Reproductive bodies in sori between hair bands that alternate successively on ventral and dorsal sides of the blade, both sporangial and oogonial sori forming concentric continuous or interrupted lines between successive ventral hair bands, leaving a sterile intercalary band. Sporangial sori non-indusiate, composed of aggregates of meiosporangia 70–110 µm indiameter usually, but not always, separated from adjacent sori by a sterile band bordered by hair bands. Oogonial sori in similar bands, the oogonia tending to be aligned in short rows along the axis of the parent blade and of similar size to sporangia (50–90 µm indiameter), but the sori indusiate. Gametophytes from Lord Howe Island dioecious; antheridia 35–40 µmlong, embedded in somewhat superficial sori.

Distribution. Known from West Africa, southern Africa, South and East Asia, islands in the Central and South Pacific Ocean and in Chile. In Australia, it occurs in W. Aust., Qld. (including the southern Great Barrier Reef) and Lord Howe I.

[After Kraft, Algae of Australia: Marine Benthic Algae of Lord Howe Island and the Southern Great Barrier Reef, 2: Brown Algae:219–220 (2009)]