Ectocarpus siliculosus (Dillwyn) Lyngb.

Scientific Description

Habit and structure. Thallus medium brown, 1–25 cm long, much and irregularly branched from the base with laterals throughout, older branches often subdichotomous, sometimes secund above but not with fasciculate lateral branch systems, attached by rhizoids from lower cells; epiphytic or epilithic, occasionally free-floating. Branches tapering gradually from the base, normally into long false hairs with few phaeoplasts and without a basal meristem. Lower filaments 20–38(–45) µm in diameter, cells L/B(0.5–)1–2; branchlets 10–15 µm in diameter, cells L/B(0.5–)1–2; false hairs 8–12(–16) µm in diameter. Growth diffuse. Cells with several elongate or ribbon-like, simple or branched and usually relatively broad phaeoplasts, each with several pyrenoids.

Reproduction.By pedicellate or occasionally sessile plurilocular sporangia (or gametangia?) scattered on the branchlets, elongate-conical to narrow-linear and sometimes surmounted by a hair, apically tapering or broader in their centre, 70–160 µm long and (12–)20–35(–50) µm in diameter; some plants also bearing ovoid to subspherical, sessile or pedicellate unilocular sporangia, (18–)25–38 µm in diameter.

Distribution. In southern Australia, along the whole coast from Rottnest I. (probably further north), W. Aust., through Vic. and Tas., into N.S.W. and to S Qld.

Habitat. E. siliculosus is a common winter species in both rough-water and sheltered conditions.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 33–34 (1987)]