Peyssonnelia tenuiderma K.R.Dixon

Scientific Description

Habit and structure. Thallus crimson-red, lacking radial striae and concentric bands, lightly calcified hypobasally, composed of thin often imbricate blades that grow largely free of the substratum, to 55 (–90) µm thick. Hypothallus composed of sparingly branched parallel filaments; cells elongate-rectangular to rhomboidal in radial vertical section, 20–48 µm long, 7–15 µm tall. Perithallus composed of assurgent filaments (2–) 3–4 cells long, the perithallial coxal cells cut off at broad angles and of similar dimensions to hypothallial cells, giving rise to 1 or 2 filaments of squat cells [L:B <1] cells dorsally. Hairs rounded or bell-shaped, roughly isodiametric, 10–15 µm diam., borne directly on perithallial coxal cells. Rhizoids unicellular, long, slender, c. 10 µm diam., cut off centrally from the ventral faces of hypothallial cells.

Reproduction. Tetrasporangial nemathecia forming scattered dark red irregularly ovoid to circular patches over the entire dorsal thallus surface, to 100 µm thick, composed of simple or branched paraphyses c. 12.5 µm diam.; lower cells ±isodiametric; distal cells distinctly shorter than wide. Tetrasporangia regularly decussate-cruciate, surrounded by a thick sporangial wall and borne on short broad cupulate unicellular pedicels. Gametophytes monoecious, with common male and female nemathecia; spermatangial filaments sometimes forming at the edges of otherwise female nemathecia. Carpogonial branches 4-celled, borne on the basal cells of paraphyses; hypogynous cells elongate; carpogonium small, conical. Auxiliary cell branches 3-celled, borne laterally on basal cells of paraphyses, the subapical cell the auxiliary cell. Branched gonimoblast filaments developing directly from the diploidised auxiliary cell, giving rise to solitary or chains of up to 3 carposporangia 37–95 µm long and 15–55 µm diam. Spermatangial initials developing in simple uniseriate chains, several from each bearing cell, later occasionally dividing anticlinally to form laterally paired mature spermatangia. Sterile paraphyses sometimes present among spermatangial filaments.

Distribution. Known only from subtidal reefs in Adele Island and Beagle Reef, north-western Australia.

[After K.R. Dixon in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 227–230 (2018)]