Peyssonnelia pseudostrata K.R.Dixon

Scientific Description

Habit and structure. Thallus reddish orange to light reddish brown, with faint to distinct radial streaks and concentric bands, partially encrusting, but with the margins remaining largely free of the substratum. Blades 155–310 µm and 7–10 cells thick, becoming thicker primarily by the elongation of the perithallial cells. Hypothallus composed of parallel radiating filaments of elongate cells with thick lower walls, typically appearing multilayered due to the migration of most cell contents to the dorsal and ventral regions of the tall hypothallial cells leaving a central vacuolate space. Perithallus moderately thick, containing both assurgent and horizontally directed trabeculate filaments. Assurgent filaments arising at 30–60° to the hypothallus, composed of elongate cells below [L:B 2.5–6] that gradually decrease in length, the 2–4 most distal cells squat [L:B <1] and deeply pigmented. Cells of the middle to upper perithallus yellow, partially to completely resistant to staining by aniline blue. Horizontal perithallial filaments of slender elongate cells arising from lower perithallial cells and traversing the middle to lower perithallus irregularly, frequently giving rise to assurgent perithallial filaments themselves. Hairs, where present, 20–38 µm long, 15–20 µm diam., embedded among the cells of the upper perithallus. Rhizoids unicellular, up to 190 µm long and 8–14 µm diam.

Reproduction. Tetrasporangial nemathecia forming small irregular patches at c. 2 cm from the thallus margin, composed of simple paraphyses of slender elongate cells (25–48 µm long and 2–6 µm diam.) below, the 2–4 most distal cells markedly shorter and broader (4–8 µm long and 7–18 µm diam.). Tetrasporangia 85–125 µm long and 52–92 µm diam., irregularly cruciately divided, often appearing tetrahedral, borne laterally on enlarged basal cells of paraphyses. Gametophytes presumably dioecious. Female nemathecia forming gelatinous patches 1–2 mm diam. on the thallus surface, composed of simple slender to beaded paraphyses c. 225 µm and 6–10 cells long. Auxiliary cell branches 5 or 6 cells long, the suprabasal cell acting as the auxiliary cell, each cell on either side of the auxiliary cell often cutting off 1 or 2 cells laterally following the diploidisation of the auxiliary cell. Gonimoblasts developing directly from the connecting filament adjacent to a diploidised auxiliary cell, maturing to produce 2 large carposporangia 32–68 µm long and 35–60 µm diam. Spermatangia not seen.

Distribution. Known only from north-western Australia.

[After K.R. Dixon in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 221−224 (2018)]