Polycoelia laciniata J.Agardh

Scientific Description

Habit and structure. Thallus medium to dark red, flat, arising from a short stipe, usually 5–20 cm high and as much across, much branched essentially in one plane in an irregularly alternate to di- or polychotomous manner, in older thalli often with marginal proliferations which may develop into foliose laterals; margin smooth in young thalli to irregular in older thalli; lower parts (0.3–)1–2 cm broad, to 4 cm broad in old thalli, usually as wide in median parts, tapering gradually or abruptly to (1–)2–4 mm broad near apices in young thalli but such tapering apices commonly lost from older plants; substance firm when fresh but becoming gelatinous, usually adhering to paper on drying and tending to disintegrate on wetting. Holdfast discoid, 1–3 mm across; epilithic or epiphytic on larger algae. Structure. Thallus 0.5–1 mm thick in median parts, consisting of a medulla of a single layer of large, thick-walled, isodiametric to slightly elongate cells which in median parts of the thallus comprise one-half to two-thirds of the thickness, and an inner cortex of a lax network of slender filaments of relatively short cells, which also grow between the medullary cells, and which produce an outer cortex of erect, branched chains of 2–5 small cells, the outermost of which are isodiametric and about 3 µm across; stellate cells absent.

Reproduction. Sexual thalli dioecious. Carpogonial branch systems monocarpogonial, scattered in the mid cortex, consisting of an elongate and often terminally lobed supporting cell bearing 2–4 elongate, irregularly clavate, subsidiary cells, one of which forms the carpogonial branch. Fusion cell lobed, producing several connecting filaments. Auxiliary cell systems scattered in the mid cortex, about 30 µm across, consisting of an enucleate auxiliary cell bearing 3–6 multinucleate, isodiametric to slightly elongate, subsidiary cells, one (rarely 2) of which may form a 1–3-celled chain. Cystocarps scattered, 0.5–1 mm across, non-ostiolate and slightly protruding, with an involucre of denser filaments and with numerous groups of subspherical carposporangia (18–26 µm across) surrounded by gonimoblast filaments. Spermatangia cut off from the outer cortical cells, 1.5–2 µm in diameter. Tetrasporangia scattered in the outer cortex, elongate-ovoid, cruciately divided, 32–45 µm long by 17–25 µm in diameter.

Distribution. South-west W. Aust., to Flinders, Vic., and around Tas.

Habitat. P. laciniata is a sublittoral species, found mainly on rough-water coasts.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 246–247 (1994)]