Peyssonnelia impermia K.R.Dixon

Scientific Description

Habit and structure. Thallus red to brownish red, with faint concentric bands and, occasionally, greenish radial striae. Plants forming thin moderately calcified prostrate blades that are closely appressed but not tightly adherent to the substratum. Mature sectioned portions of the perithallus resistant to staining with aniline blue, the hypothallus readily staining. Hypothallus composed of rarely branched parallel filaments; cells rhomboidal to rectangular in radial vertical section, 25–45 µm long and 22–25 µm tall. Perithallus composed of short (mostly 3- or 4-celled) assurgent filaments, the large broadly attached basal perithallial coxal cell giving rise to 2 narrower assurgent filaments, the proximal filament typically remaining unbranched and the distal one usually once-branched from the cell above the coxal cell. Ultimate cells of perithallial filaments typically packed with many small rhodoplasts. Towards the margin, hypothallial and lower perithallial cells ±vacuolate. Mature cells densely packed with small discoid starch grains. Hairs absent. Rhizoids unicellular, to 60 µm long and 8 µm diam., cut off the lower distal corners of hypothallial cells.

Reproduction. Tetrasporangia irregularly or decussate-cruciately divided, borne in gelatinous nemathecia composed of mostly 4-celled paraphyses, 1 or 2 from each ultimate perithallial cell, the lower 2 cells slender and elongate, 12–28 µm long and 2–3 µm diam.; uppermost cells small, ±isodiametric, c. 8 µm diam., rounded and with thickened pale brown walls. Tetrasporangia terminating 1-celled cupulate pedicels borne directly from ultimate perithallial cells, initially small and elongate, swelling to c. 45 µm diam. at maturity. Gametangia not seen.

Distribution. Known only from the Kimberley coast, north-western Australia.

[After K.R. Dixon in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 217−220 (2018)]