Melanothamnus ferulaceus (J.Agardh) Díaz-Tapia & Maggs

Scientific Description

Habit and structure. Thallus mostly upright, to 30 mm tall, with limited prostrate axes attached by rhizoids that are pit-connected to bearing cells, pale brown. Primary axes percurrent, bearing alternate to subdichotomous lateral branches every 6–9 segments; lateral branches more sparsely branched (every 10–16 segments); minor branches slightly curved towards the bearing branch. Axes of lower thallus 220–300 µm diam. [segment L:B c. 1]; mid-thallus 200–250 µm diam. [segment L:B 0.5–1]; upper thallus tapering to 100–200 µm diam. [segment L:B 0.3–0.6], markedly broader than long near apices. Apices abruptly tapering to a point. All segments with a rounded wall and slight constriction at joints, with 4 pericentral cells and a trichoblast/scar cell, the latter in a spiral pattern with a 1/4 divergence. Trichoblasts well developed near apices, 500–750 µm long, subdichotomously divided 4 or 5 times, lower cells 15–30 µm diam. [L:B 3–5], tapering gradually to upper filiform cells c. 5 µm diam.

Reproduction. Spermatangia in cylindrical heads on lower dichotomy of trichoblasts, 250–300 µm long, 60–80 µm diam., with a prominent sterile apical cell. Cystocarps spherical, 250–360 µm diam., with clavate carposporangia 70–100 µm long and 30–35 µm diam. at the broadest point. Tetrasporangia in spiral sequence in upper branches, spherical, 70–120 µm diam., tetrahedrally divided.

Distribution. Widely distributed, most common in tropical seas.

Habitat. epilithic or epiphytic in the intertidal or shallow subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 542 (2018)]