Ulva rigida C.Agardh

Scientific Description

Habit and structure. Thallus dark green below, lighter above, epilithic or on seagrasses (e.g. Amphibolis), 4–20(–30) cm high, with several broad fronds from the holdfast, usually much and irregularly divided and lacerate or lobed, 1–6 cm across, margin entire, surface smooth. Cells in surface view arranged in short rows above, soon becoming irregularly arranged, isodiametric to elongate, 10–20(–25) µm broad and 20–25(–30) µm long, basal rhizoid-producing cells larger; pyrenoids 1(–2) per cell. Thallus 45–60(–70) µm thick in upper parts with cells in sectional view L/B about 1(–1.5) and 18–25 µm long, 80–110 µm thick in mid and lower parts with cells L/B 1.5–2(–2.5) and 22–40 µm long, and (120–)200–250(–300) µm thick near the base with a broad central mass of dense rhizoids, with cells L/B 1–1.5(–2) and 25–40 µm high.

Reproduction. Not recorded.

Distribution. Common in southern Australia, from Whitfords Beach (Perth), W. Aust., to Avoca Beach, N.S.W. and around Tasmania.

Habitat. On coasts of strong to moderate wave action, just above and below low tide level.

[After Womersley, Mar. Benthic Fl. Southern Australia I: 141-142 (1984) as Ulva australis]