Peyssonnelia atricolor K.R.Dixon

Scientific Description

Habit and structure. Thallus dark maroon, at times almost black, smooth, lacking radial striae and concentric bands, brittle and heavily calcified both within the thallus and as a thick hypobasal layer of similar thickness to the vegetative tissue; consisting of spreading blades that follow the contours of the substratum, but are not completely adherent across their entire undersurface, 200–450 µm and 16–22 cells thick. Hypothallus composed of parallel often curved radiating filaments. Perithallus with upper and lower layers when mature. Lower perithallial filaments arising at narrow angles (30–60°) and consisting of obovate to elongate, rectilinear or somewhat undulate cells. Among the assurgent filaments, horizontally directed filaments traverse the lower perithallus obliquely, these absent from the upper layer. Mature thalli thickened by an upper perithallial layer composed of vertical filaments of proximally constricted cells. Hairs absent. Rhizoids unicellular, elongate, to 200 µm long, c. 10 µm diam.

Reproduction. Reproduction not observed.

Distribution. A widespread endemic in the Kimberley region, N.W.A., ranging from Brue Reef in the south to Long Reef off Cape Bougainville in the northernmost Kimberley.

[After K.R. Dixon in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 230 –231 (2018)]