Peyssonnelia rainboae K.R.Dixon

Scientific Description

Habit and structure. Thallus lightly to moderately calcified, crimson-red, with distinct, often bright yellow radial striae and faint concentric bands, the striae particularly apparent when dry. Lobes decumbent and often imbricate, mostly free of the substratum and easily removed. Blades mostly thin at the margins, up to 350 µm and 14 cells thick proximally. Hypothallus uniaxial, composed of largely unbranched lower-order filaments arising subalternately from the relatively large-celled axial filaments that are slightly inset from the ventral surface. Perithallus with distinct upper and lower zones. Lower perithallus of filaments arising at narrow angles (30–40°) to the hypothallus, up to 60° when older, the cells large (20–50 µm long, 12–30 µm diam.), rounded-rectangular and typically trabeculate. Upper perithallus of relatively small (5–10 µm diam.), short (to 10 µm long), deeply pigmented cells that form vertical files towards the dorsal surface. Large inflated hyaline cells scattered near the junction of upper and lower perithalli. Hairs absent. Rhizoids multicellular, unbranched, to 250 µm long and c. 20 µm diam., the proximal rhizoidal coxal cell usually remaining completely within the ventral cuticle.

Reproduction. Tetrasporangia large, 140–190 µm long and 40–75 µm diam. at maturity, somewhat clavate, borne laterally on enlarged basal cells of long slender paraphyses c. 5 µm diam. Gametangia 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: 224−227 (2018)]