Herposiphonia parca Setch.

Scientific Description

Habit and structure. Thallus red, the prostrate axes attached by elongate unicellular rhizoids with digitate tips, arising from the distal ends of ventral pericentral cells. Indeterminate axes with circinate apices, with a regular sequence of 3 determinate and 1 indeterminate lateral branches; determinate axes arising dorsally or dorso-laterally, but erect; indeterminate axes ventrolateral and prostrate. Prostrate axes 85–100 µm diam. [segment L:B 1–1.2], with 8–10 pericentral cells. Determinate branches to 1.3 mm and 8–12 segments long, 60–85 µm diam. [segment L:B 1–2]. Basal segment with 4 pericentral cells, others with 8 or 9 pericentral cells. Trichoblasts arising exogenously and laterally from the dorsal surface of a developing determinate lateral, 2–3 cells from the branch apex, initially secundly branched but appearing dichotomous when mature, becoming conspicuous, to 700–850 µm long, proximal cells 35–50 µm diam. [L:B 1–2], tapering to more slender elongate distal cells, 8–12 µm diam. [L:B 10–20].

Reproduction. Spermatangia in elongate-cylindrical heads borne in clusters of 4 or 5 at apices of determinate branches, adjacent to trichoblasts, with a 1- or 2-celled stalk and a fertile portion 9 or 10 cells and 170–220 µm long, 45–50 µm diam., with a terminal unbranched filament 1–3 cells long. Other reproductive structures not observed.

Distribution. Widespread in the Indian and Pacific Oceans; also recorded as an introduction to the Mediterranean.

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: 517–518 (2018)]