Polystrata erupta K.R.Dixon

Scientific Description

Habit and structure. Thallus pink, heavily calcified and brittle, forming tightly adherent closely appressed crusts on coral and rock. Plants composed of numerous layers of spreading overgrowing blades that continually initiate from the mesothallus of the underlying layer. Mesothallus consisting of radiating filaments of mostly rounded cuboid cells, these giving rise to a thin (25–75 µm and up to 6 cells thick) dorsal perithallus of rounded ±isodiametric cells and a monostromatic ventral perithallus of squat cells 4–10 µm long and 8–18 µm diam. [L:B mostly <0.5]. Dorsal perithallus composed of ±isodiametric cells 12–20 diam. below (among which cell fusions were not observed), and much smaller (3–6 µm diam.) often elongate cells above; terminal cells often flattened. Hairs deltoid, 25–33 µm long and 15–23 µm diam. Cells of the ventral perithallus, mesothallus and lower dorsal perithallus densely packed with discoid floridean starch grains up to 5 µm diam., these not noticeable in the deeply pigmented upper cells of the dorsal perithallus.

Reproduction. Tetrasporangial nemathecia partially immersed in the dorsal perithallus, forming uncalcified dark brown to black spots to 1 mm diam. on the upper surface and composed of unbranched or basally branched paraphyses to 7 cells and 100 µm thick; cells 7–15 µm long and 2–5 µm diam. Tetrasporangia borne on simple unicellular cupulate pedicels that develop directly from the ultimate cell of the underlying dorsal perithallus, regularly decussate-cruciately divided, 27–65 µm long and 15–35 µm diam. Gametangia not seen.

Distribution. Known from Adele Island, north-western Australia, and the Philippines, although it is probably more widespread in the tropics.

[After K.R. Dixon in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 232–235 (2018)]