Actinotrichia fragilis (Forssk.) Børgesen

Scientific Description

Habit and structure. Thallus to 7 cm high, grey-pink to orange-red, forming a hemispherical or spreading clump, subdichotomously branched at intervals of 2–10 mm. Axes 250–600 µm in diameter; emergent filaments either absent, randomly arranged, or in whorls at intervals of 150–200 µm. Medullary filaments 5–12 µm in diameter. Cortex 3 or 4 cells thick; inner cells 22–32 µm in diameter, with occasional lateral fusions; epidermal cells turbinate, 20–27 µm in diameter; emergent filaments cylindrical, to 550 µm long, with cells 10–13 µm in diameter.

Reproduction. Spermatangial cavities 150–250 µm in diameter; spermatangia spherical to obovoid, c. 5 × 7 µm. Cystocarps not observed. Tetrasporangia subspherical, 25–27 × 22–25 µm.

Distribution. Known from Coral Bay, W.Aust., presumably across northern Australia to the Great Barrier Reef, Qld. Widespread in tropical seas.

Habitat. A. fragilis growson rock or coral platforms in the subtidal.