Seiria magnifusa K.R.Dixon

Scientific Description

Habit and structure. Thallus dark crimson-red to maroon, broadly lobed, the distally free blades heavily calcified and with raised concentric bands. Hypothallus multiaxial, composed of sparingly branched parallel filaments of cells 20–38 µm long and 10–15 µm tall in profile. Perithallus thin, of short filaments mostly 6–8 cells long, the cells with thick calcified walls. Perithallial basal coxal cells fusing horizontally with adjacent cells perpendicular to the underlying hypothallial filaments; mid-perithallial cells becoming fused to adjacent cells primarily in a radial direction and appearing irregularly cuboid to horizontally elongate in radial vertical section. The uppermost 2 perithallial cells unfused, roughly isodiametric, 5–10 µm tall and 7–10 µm diam. Hair filaments absent or indistinct. Rhizoids unicellular, long and slender, 5–10 µm diam. and up to 100 µm long.

Reproduction. Tetrasporangia borne on enlarged goblet-shaped pedicels with lateral paraphyses, usually developing in series, occasionally simultaneously. Tetrasporangial initial usually cutting off a single cell distally which can divide once more or remain whole. Mature tetraspores highly variable in shape and size, soon degenerating. Tetrasporangial initials either dividing once more to form irregularly cruciate tetrasporangia, cutting off a lateral cell that will become 1 or 2 mature tetrasporangia, or reverting back to vegetative development and continuing growth as a paraphysis with 1 or 2 lateral degenerate tetraspores. Nemathecia raised, gelatinous, scattered on the thallus surface, composed of simple paraphyses up to 7 cells and 100 µm long, the middle and lower cells elongate-ovoid or rectilinear; terminal cells squat [usually with L:B 0.5–1], distally free. Gametangia not observed.

Distribution. Known only from Adele Island in the Kimberley region, north-western Australia.

[After K.R. Dixon in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 241 (2018)]