Pollexfenia lobata (Hook.f. & Harv.) Falkenb.

Scientific Description

Habit and structure. Thallus erect, red-brown, 10–30 cm high, membranous, complanately branched, main branches (0.5–)1–1.5(–2) cm broad, with irregularly positioned laterals of similar or lesser width, branch apices rounded, margins smooth to irregular, with a central, prominent, midrib commencing from near apices to well down the thallus; fronds denuded below leaving the thickened midrib as a stalk 1–2 mm thick, often with small proliferous blades. Holdfast discoid, 2–5 mm across; epilithic. Structure. Branch apices with numerous apical cells producing congenitally fused systems, with the axial cells cutting off 4 pericentral cells, 2 on each side; apical cells hemispherical to conical, 7–12 µm in diameter, axial cells branching usually 2 cells apart, with unicellular primordia (some becoming multicellular and branched) cut off from the alternate cells on alternate sides of the thallus. Mature fronds have the apical margins apparently non-functional and coloured brown for 6–10 cells deep, this margin often split. The pericentral cells divide laterally giving 3–5 between adjacent veins, and also show transverse divisions with 6–10 corresponding to each mature axial cell; mature surface (derivative) cells are mostly 35–45 µm in diameter and 30–60(–90) µm long, L/D mostly 1–1.5, and become irregularly arranged in surface view. Fronds 2 cells thick, with the midrib formed by proliferation of cortical cells from the pericentral cell derivatives. Trichoblasts much branched, situated on the thallus surface above the axial cells, with the basal part becoming polysiphonous. Cells probably uninucleate; rhodoplasts discoid to elongate.

Reproduction.Associated with the trichoblast tufts. Gametophytes dioecious. Procarps on lower trichoblast cells, with 4-celled carpogonial branches. Carposporophytes branched, with clavate terminal carposporangia 20–40 µm in diameter. Cystocarps ovoid, short-stalked, 800–1200 µm in diameter; pericarp ostiolate, 2 cells thick, ecorticate, outer cells isodiametric, 50–90 µm across. Spermatangial organs on branches of trichoblasts, their stalks becoming polysiphonous, 90–160 µm in diameter and 200–400 µm long, ends rounded or tapering, with single sterile apical and basal cells, spermatangia ovoid, 5–7 µm in diameter. Stichidia on the basal, polysiphonous, part of trichoblasts, 120–200 µm in diameter and 500–750 µm long, corticated, with tetrasporangia in a close spiral, one per segment, 70–110 µm in diameter, with 2 cover cells.

Distribution.Houtman Abrolhos, W. Aust., to Walkerville, Vic., and around Tas; doubtfully Qld.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 355–357 (2003)]