Chiracanthia arborea (Harv.) Falkenb.

Scientific Description

Habit and structure. Thallus dark red-brown, 10–40 cm high, with a single or several axes bearing long main laterals irregularly radially, with lesser branches clothed sparsely to densely with short determinate laterals. Holdfast discoid, 2–8 mm across; epilithic, epiphytic, or on shells or jetty piles. Structure. Apex enclosed by determinate branchlets, forming 4 pericentral cells and becoming corticated from close to apices. Axes 1–2 mm in diameter below, above 0.5–1 mm in diameter. Determinate branchlets 0.8–2.5 mm long, ecorticate, with 3–4 basal branches each 0.5–1.5 mm long and 40–120 µm in diameter, tending to lie in one plane, with 4 pericentral cells and segments L/D 0.5–1.3, tapering to a single apical cell sometimes extended to a monosiphonous filament 5–10 cells long; trichoblasts rare, caducous; a darkly-staining animal endophyte frequent. Rhodoplasts discoid.

Reproduction. Gametophytes dioecious. Procarps borne on branches of determinate branchlets. Carposporophytes branched with elongate-ovoid to clavate terminal carposporangia 35–55 µm in diameter. Pericarp ostiolate, without a neck, 2(–3) cells thick, basally slightly corticate. Cystocarps sessile on determinate branchlets, ovoid, 0.5–1 mm in diameter. Spermatangial branches terminating determinate branchlets, with monosiphonous pedicels 1–3 cells long and with 1–3 sterile apical cells, fertile parts 90–200 µm long and 40–90 µm in diameter. Tetrasporangia borne in elongate branches of determinate branchlets 0.5–1.4 mm long and 90–130 µm in diameter, with undulating margins due to the tetrasporangia which occur one per segment, spirally arranged, subspherical, 60–90 µm in diameter, with 2–3 rectangular cover cells.

Distribution.Geographe Bay, W. Aust., to Port Phillip, Vic., and N Tas.

Habitat. Usually in moderately deep water.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 233–235 (2003)]