Rhodophyllis volans Harv.

Scientific Description

Habit and structure. Thallus erect to decumbent, 5–10(–12) cm high, complanately and subdichotomously branched with flat branches (2–)3–4(–6) mm broad throughout and 200–400 µm thick, tapering only slightly above, with the margins bearing irregular, spathulate, basally constricted branchlets 2–3(–5) mm long, together with spiny outgrowths on some older branches, apices broad and rounded but with an apical notch; microscopic vein system visible after staining. Holdfast fibrous; epilithic. Structure uniaxial, with the axial and periaxial filaments enlarging as a pinnate vein system; medulla slight, cortex 1–3(–4) cells thick, inner cells ovoid and 40–80 µm in diameter, with rosettes fairly distinct, cells 8–12 µm in diameter. Rhodoplasts discoid, becoming ribbon shaped and branched.

Reproduction. Sexual thalli dioecious; procarpic. Carpogonial branches 3-celled, borne on outer cortical cells on the surface of young branches, lying parallel to the surface with reflexed trichogynes, with the adjacent cortex thickening. Post-fertilization events as in R. membranacea, producing a carposporophyte with a central fusion cell, radiating gonimoblast filaments with terminal chains of ovoid carposporangia 18–27 µm in diameter and inner nutritive tissue; cystocarps protruding, on the surface of the proliferations or scattered on the branch surfaces, 400–1200 µm across, non-ostiolate. Spermatangia unknown. Tetrasporangia scattered in the cortex of young branches, ovoid, 18–26 µm in diameter, zonately divided.

Distribution.Champion Bay, W. Aust., to Walkerville, Vic., and the N coast of Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 417–419 (1994)]