Platysiphonia delicata (Clemente) Cremades

Scientific Description

Habit and structure. Thallus medium to dark red-brown 0.5–1.5(–3) cm high, erect or forming a turf-like mat in the uppermost sublittoral, with basal prostrate branches producing erect, moderately to much divided, branches. Attachment by rhizoidal holdfasts or by stout unicellular rhizoids with multicellular haptera, arising from the flanking cells of prostrate filaments; epilithic or epiphytic on Posidonia or various algae. Structure. Apical cell hemispherical, forming first the abaxial pericentral cell, followed by 2 lateral pericentral cells (each forming 2 flanking cells) and last the adaxial pericentral cell. Mid branches 80–100 µm broad, segments L/D 0.8–1. Lower thallus ecorticate or very lightly corticate, 150–200 µm broad. Cells uni-nucleate; rhodoplasts discoid.

Reproduction. Gametophytes dioecious. Procarps occur on the adaxial surface of young lateral branches which develop further rapidly, with the adaxial pericentral cell producing at first a sterile cell and a 4-celled carpogonial branch followed by a second cell. Carposporophyte moderately branched, with a relatively slight basal fusion cell and clavate terminal carposporangia 20–25 µm in diameter. Cystocarps sessile, ovoid to urceolate, 300–500 µm across; pericarp ostiolate, arising after fertilisation, with about 15 erect filaments, each cell cutting off 2 outer transversely elongate pericentral cells only, thus 2 cells thick. Spermatangial blades developed from small lateral branches, with initials and spermatangia cut off from lateral (and sometimes transverse) pericentral cells, but usually with sterile transverse pericentral cells and flanking cells, 0.5–1 mm long and 120–200 µm broad. Tetrasporangial stichidia developed as lateral branches, ecorticate with 2 longitudinal rows of tetrasporangia cut off from the lateral pericentral cells, followed by the abaxial cover cell and lastly the adaxial cover cell, with the flanking cells dividing horizontally into 2 cells which become curved and partly protect the tetrasporangia which are subspherical and 40–65 µm in diameter.

Distribution.Spain; tropical eastern Atlantic Ocean; tropical Indian Ocean; Qld. In southern Australia, from Rottnest I., (and Houtman Abrolhos), W. Aust., to Walkerville, Vic., and N Tas, extending through NSW and Qld.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 158–160 (2003)]