Hypnea spinella (C.Agardh) Kütz.

Scientific Description

Habit and structure. Thallus to 10 cm tall, yellow to dark red, forming bushy clumps with no distinct primary axes, irregularly dichomously branched, widely divaricate, some branches curving upwardly and appearing cervicorn. Axes 0.5–1.0 mm diam., tapering to acute tips; most axes with a moderate covering of short spinous branchlets, these directed towards the apex, broader at the base and tapering. Axial filament prominent, surrounded by 1–3 layers of large hyaline medullary cells. Cortex with 1–3 layers of smaller pigmented cells, sharply demarcated from medullary cells; outer cells angular in surface view, mostly vaguely longitudinally aligned, 12–20 µm long, 5–12 µm wide.

Reproduction. Tetrasporangial nemathecia on middle to basal parts of fertile lateral branchlets, initially oval and on one side of bearing branch, 550–750 µm long, 300–500 µm wide, but eventually encircling the branch. Tetrasporangia ellipsoidal to obovoid, 30–40 µm long, 20–26 µm diam., zonately divided. Other reproductive structures not seen.

Distribution. Widespread in tropical seas.

Habitat. Epilithic or epiphytic in the shallow subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 173–174 (2018)]