Melanothamnus infestans (Harv.) Huisman

Scientific Description

Habit and structure. Thallus red, primarily erect, to 16 mm tall, or with limited prostrate axes, attached to the substratum by unicellular digitate rhizoids arising from the basal cells of primary axes. Erect axes subdichotomously branched every 5–10 segments. Axes with 4 pericentral cells and a trichoblast/scar cell on each segment in a spiral pattern with a 1/4 divergence between successive segments. Lower segments 390–430 µm diam. (including a wall to 100 µm thick) [L:B 0.4–0.5 (c. 1 if the wall is excluded)]; mid-thallus segments 100–170 µm diam. [L:B 1–1.3 (–3)], tapering gradually to upper segments 40–75 µm diam. [L:B 1–1.2]. Lateral branches replacing trichoblasts.

Reproduction. Spermatangia in cylindrical to lanceolate heads forming as one branch of a basal dichotomy of trichoblasts, 170–290 µm long, 40–45 µm diam., with or without a sterile apical cell. Cystocarps stalked, spherical to ovoid, not urceolate, to 440 µm diam. Carposporangia clavate or lachrymiform, 20–30 µm diam. Tetrasporangia in spiral series in upper branches, 30–60 µm diam., distorting the bearing branch.

Distribution. Widespread in Australian seas and also recorded from Indonesia.

Habitat. epilithic or epiphytic in the intertidal and subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 543–545 (2018)]