Melanothamnus gigas Huisman

Scientific Description

Habit and structure. Thallus large, to 40 cm tall, profusely branched; lower axes to 5 mm wide, tapering to the 150–200 µm diam. upper axes, then rather abruptly to straight pointed apices. Trichoblasts present but often rudimentary, soon dehiscent, leaving a scar cell. Trichoblasts/scar cells 1 per segment in a spiral pattern with a 1/4 divergence. Lateral branches not associated with trichoblasts. Axes with 4 pericentral cells, heavily corticated, the cortication beginning 10–12 cells from the apex, arising from lower corners of pericentral cells. Pericentral cells forming a gentle clockwise spiral (distally from apex).

Reproduction. Spermatangia forming in cylindrical heads on lower branch of trichoblasts, with a terminal sterile filament several cells long. Cystocarps subspherical, 700–950 µm diam. Carposporangia clavate, 150–220 µm long, 80–120 µm diam. Tetrasporangia is spiral series of up to 9 sporangia, spherical, 120–145 µm diam., tetrahedrally divided, when mature markedly distending the bearing segment.

Distribution. Known only from the vicinity of Barrow Island.

Habitat. epilithic in the subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 542–543 (2018)]