Herposiphonia elongata M.Masuda & K.Kogame

Scientific Description

Habit and structure. Thallus red, with prostrate indeterminate and erect determinate axes, attached by unbranched unicellular rhizoids arising from the distal end of ventral pericentral cells. Indeterminate prostrate 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 ventro-lateral and prostrate. Prostrate axes terete, 100–110 μm diam. [segment L:B c. 1], with 9 or 10 pericentral cells. Determinate branches initially curved but straightening, unbranched, 1.5–2.5 mm long, with 9–22 segments when mature, terete, 60–75 μm diam. [segment L:B mostly 1–4], with 6–9 pericentral cells. All determinate axes with 1–5 distal trichoblasts forming in a spiral sequence, these dichotomously divided, with tapering unpigmented cells. Cells with numerous spherical plastids, these often pectinate.

Reproduction. Spermatangia in elongate-cylindrical to cone-shaped heads, 1–3 replacing trichoblasts in a spiral pattern at apices of determinate branches, with a 1- or 2-celled stalk and a fertile portion 7 or 8 cells and 150–200 μm long, 45–55 μm diam., with a terminal unbranched filament 3–6 cells long. Cystocarps terminal on determinate axes, 480–580 μm diam., the subtending determinate branch thickening slightly. Tetrasporangia in linear series of 3–9 in determinate axes, 1 sporangium per segment, spherical, 45–60 μm diam.

Distribution. Known from Malaysia and Japan. Widespread in north-western Australia.

Habitat. Generally epiphytic.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 511–514 (2018)]