Phloiocaulon spectabile Reinke

Scientific Description

Habit and structure. Thallus medium to dark brown, (5–)8–16 cm long, with one to several axes from a small discoid base 0.5–1.5 mm across; axes dark brown to almost black, smooth, often denuded of laterals below, and above bearing numerous alternate, dense, fasciculate tufts along the main lateral branches; epilithic. Branching of several orders, radial or often subdistichous near the apices with laterals every 2–4 segments, with lesser laterals determinate and tapering to a point over their last few segments; laterals with a single, large, inner cell (later subdivided) and a single-layered cortex of elongate cells which divide transversely, and usually again, to give a row of four cells per segment; loose descending rhizoids absent, but appressed rhizoidal secondary cortication developing at base of lateral tufts; phaeophycean hairs in clusters in axils of laterals, lost from older parts. Axes (300–)500–800 µmin diameter, with a smooth-surfaced secondary cortex of cells which enlarge and on oldest axes cut off radially chains of smaller cells forming an outer secondary cortex; uncorticated laterals 80–120 µmin diameter with segments L/B(0.5–)0.8–1.0; determinate laterals 70–80 µmin diameter for most of their length with segments L/B0.6–1.0, shorter near the tips.

Reproduction. Unilocular sporangia 1–2(–3) in axils of laterals, subtended by two, opposite, simple or once (–2) branched bracts, usually inwardly curved, positioned at right angles to the axis and lateral; sporangia with a short, 1–3 celled pedicel, sub-spherical, (50–)70–90(–105) µmin diameter. Sexual plants with small mixed clusters of macro- and microgametangia borne similarly to the sporangia but subsessile on a small, multicellular pad; macrogametangia subspherical, 60–120 µmin diameter, with loculi 4–6 µmacross; microgametangia subspherical to ovoid, (80–)100–140 µmacross, with loculi 2–4 µmacross.

Distribution.From Geographe Bay, W. Aust., around southern Australia to Lorne, Vic., and NW Tas.

Habitat. P. spectabile is typically a deeper water alga, known from the drift and to 25 m deep; specimens from shaded upper sublittoral pools are usually more densely tufted and sterile.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 182–184 (1987)]