Polysiphonia constricta Womersley

Scientific Description

Habit and structure. Thallus mostly upright, to 30 mm tall, with a limited prostrate axis attached by unicellular rhizoids, these pit-connected to the bearing cell. Apices slightly sinuous. Lateral branches associated with basal cells of trichoblasts, arising every 7–13 segments. Axes ecorticate, with 6 or 7 pericentral cells, 400–500 µm diam. near base [segment L:B 0.2–0.3], tapering to ±300 µm diam. mid-thallus [segment L:B c. 0.4], then to 50–75 µm diam. near apices [segment L:B 0.5–1]. Lateral branches generally thinner at the base. Trichoblasts sparsely to well developed, to 400 µm long, dichotomously divided, mostly dehiscent. Trichoblasts/scar cells generally every 3–5 segments, with a 1/6 divergence.

Reproduction. Spermatangial heads forming as 1 branch of a trichoblast basal dichotomy, although the trichoblast branch is often shed and the spermatangial head then appearing terminal. Cystocarps spherical, 400–600 µm diam. Tetrasporangia in mostly linear series of up to 18, often in shorter series that are rotated slightly relative to adjacent series, to 55 µm diam.

Distribution. Known from southern Australia and Coffs Harbour in northern New South Wales. In north-western Australia from the North West Cape region to the Dampier Archipelago.

Habitat. epilithic or epiphytic in the subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 564–565 (2018)]