Predaea weldii Kraft & I.A.Abbott

Scientific Description

Habit and structure. Thallus erect, pale to medium red (often with iridescent orange tips in situ), to 9 cm tall, mucilaginous, attached by a discoid holdfast. Branches terete to slightly compressed, richly divided, with numerous lobes. Cortex of loosely associated filaments, pseudodichotomously branched every 1 or 2 cells, with the cells cylindrical, rectilinear, 12–18 µm long, 3–5 µm diam., often with simple to sparingly branched lateral adventitious filaments, these with slender cells 2.0–2.5 µm diam. Vesicular cells absent.

Reproduction. Monoecious. Spermatangia in sparse tufts on outer cortical cells, c. 2 µm diam. Carpogonial branches lateral on cortical filaments, 3-celled, the hypogynous cell subspherical; following fertilisation connecting filaments arising directly from the carpogonium. Auxiliary cells transformed vegetative cells, clearly differentiated, clavate to obovoid, 20–30 µm long, 12–14 µm diam., with a prominent apical bulge. Cells distal and proximal to the auxiliary cell differentiated, each bearing 3–6 clusters of 1–3 spherical nutritive cells 5–12 µm diam. Nutritive cells and the cells bearing them with 1 (–2) prominent spherical pyrenoids. Connecting filaments branching near the auxiliary cell, the branch terminating at and fusing with the lateral surface of the auxiliary cell and effecting diploidisation. Gonimoblast initial arising from the apex of an auxiliary cell, forming 1 or 2 subspherical to ovoid gonimolobes 100–150 µm diam., composed entirely of carposporangia 5–8 µm wide. Other reproductive structures not observed.

Distribution. Widespead in tropical to subtropical seas.

Habitat. Generally epilithic in the subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 269 (2018)]