Pollexfenia pedicellata Harv.

Scientific Description

Habit and structure. Thallus erect, red-brown, 5–20 cm high, membranous, complanately branched, main branches with lobed to elongate lateral branches, 5–12 mm broad in plants on rough-water coasts and 2–4 mm broad in some plants on sheltered coasts; branch apices rounded. Holdfast an expanding, clasping, pad; usually epiphytic on Amphibolis, occasionally on Posidonia, possibly epilithic. Structure. Branch apices with numerous apical cells producing congenitally fused systems, the axial cells cutting off 4 pericentral cells, 2 on each surface; axial cells branched usually 2 cells apart, with unicellular primordia (becoming multicellular) cut off from the alternate cells on alternate sides of the thallus; apical cells squat, 8–16 µm in diameter, the axial cells branching every few cells. Mature pericentral cell dividing transversely with 4–8 derivatives corresponding to each axial cell in length, 30–80(–100) µm in diameter and 70–180 µm long, L/D mostly 1.5–2. Thallus 2 cells thick and without a defined midrib. Trichoblasts in branched tufts, above and arising from the axial primordia, on alternate sides of the thallus. Cells probably uninucleate; rhodoplasts discoid, chained in larger cells.

Reproduction.Reproductive structures are associated with the trichoblast tufts on the axial primordia. Gametophytes dioecious. Procarps on a branch of the trichoblasts, with a 4-celled carpogonial branch. Carposporophytes with a basal fusion cell and much branched gonimoblast with clavate terminal carposporangia 25–40 µm in diameter. Cystocarps ovoid, short-stalked, 700–1000 µm in diameter; pericarp 2 cells thick, ecorticate, outer cells isodiametric (20–)45–60 µm across. Spermatangial organs as a branch of trichoblasts, elongate-ovoid, 80–150 µm in diameter and 120–270 µm long, with usually single basal and apical sterile cells, spermatangia ovoid, 8–10 µm in diameter. Stichidia in tufts associated with trichoblasts, 180–300 µm in diameter and 400–700 µm long, ecorticate, with tetrasporangia in a close spiral, one per segment, 50–90 µm in diameter, with 2–3 cover cells.

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

Habitat. P. pedicellata is a common and distinctive alga, varying considerably in branch width, broad on rough-water and moderate coasts to slender in calm conditions.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 352–355 (2003)]