Shepleya australis (J.Agardh) Gordon-Mills

Scientific Description

Habit and structure. Thallus red-brown, prostrate with axes creeping along the host (usually Pterocladia lucida) branches, branching opposite or alternate; attachment by haptera; epiphytic. Structure. Subapical cells producing opposite, distichous pairs of whorl-branchlets, axial cells enlarging to 180–190 µm in diameter and 400–500 µm long near the base; whorl-branchlets 500–1000 µm long, oppositely and distichously branched in the plane of the host surface, with the basal cell usually producing 1–3 more laterals in the plane of branching; terminal cells with rounded ends, median cells 55–85 µm in diameter and L/D 2–4; haptera in opposite pairs from the lower ends of axial cells. Indeterminate branches develop by continued growth of whorl-branchlets. Cortication absent. Cells multinucleate; rhodoplasts discoid to elongate.

Reproduction. Gametophytes dioecious. Female axis 4–12 cells long, arising at branch apices, with the last 3 cells shorter. Procarps as in Shepleya wattsii with the subapical cell bearing a sterile pericentral cell, a fertile pericentral cell producing the second auxiliary cell, and the supporting cell with an apical sterile cell and lateral carpogonial branch. The fusion cell is furcate, cutting off small gonimoblast cells with ovoid to pyriform terminal (and subterminal) carposporangia 40–90 µm in diameter; the apical cell and sterile pericentral cell divide after fertilization to form 2 inner involucral branchlets while the subhypogenous cell bears 3 outer involucral filaments which together with the inner branches curve up and around the carposporophyte. Spermatangial heads are slightly ovoid and 70–110 µm in diameter, borne on curved cells of the whorl-branchlets. Tetrasporangia are sessile on upper cells of whorl-branchlets where free from the host edge, 50–90 µm in diameter, tetrahedrally divided.

Distribution.Rottnest I., W. Aust., to Port Phillip, Vic. South Africa.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 88–92 (1998)]