Polystrata kimberleyensis K.R.Dixon

Scientific Description

Habit and structure. Thallus brown to pinkish red, heavily calcified and brittle, often almost completely covering broken coral debris as tightly adherent closely appressed crusts composed of many layers (up to 28 observed) of overgrowing blades, each arising from the distal perithallial cells of the layer beneath. Blades composed of a spreading mesothallus that gives rise to a dorsal perithallus up to 100 µm thick and a thin ventral perithallus up to 15 µm thick (including the ventral cuticle). Dorsal perithallus composed of large (7–13 µm diam.) round starch-filled lower cells that are occasionally fused laterally to one another, and smaller (c. 5 µm diam.) cells above. Ventral perithallus composed of one layer of squat cells 2–10 µm long and 7–20 µm diam. Hairs occasional in new blades, frequent in the older underlying blades, ±isodiametric, 17–25 µm diam., borne on mid-perithallial cells, vacuolate; cytoplasm pushed to the proximal end or periphery of hair cells. Tetrasporangial nemathecia appearing partially immersed, forming small rounded c. 1 mm diam. black patches that are scattered on the dorsal thallus surface. Nemathecia consisting of simple or basally branched paraphyses of up to 9 small cells; terminal cells isodiametric and rounded; lower cells mostly slightly elongate. Mature tetrasporangia 37–45 µm long and 17–33 µm diam., cruciately divided and terminal on enlarged unicellular cupulate pedicels that themselves are borne directly on terminal dorsal perithallial cells and lack associated paraphyses. Gametangia not seen.

Reproduction. Tetrasporangial nemathecia appearing partially immersed, forming small rounded c. 1 mm diam. black patches that are scattered on the dorsal thallus surface. Nemathecia consisting of simple or basally branched paraphyses of up to 9 small cells; terminal cells isodiametric and rounded; lower cells mostly slightly elongate. Mature tetrasporangia 37–45 µm long and 17–33 µm diam., cruciately divided and terminal on enlarged unicellular cupulate pedicels that themselves are borne directly on terminal dorsal perithallial cells and lack associated paraphyses. Gametangia not seen.

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

[After K.R. Dixon in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 235–236 (2018)]