Scytosiphon lomentaria (Lyngb.) Link

Scientific Description

Habit and structure. Thallus medium to dark brown, erect, 5–30(–76) cm high, terete and hollow and often constricted at intervals of 1–3 cm, or compressed to varying degrees and partly hollow or with the sides adjacent but easily separated, (0.5–)1–5(–8) mm in diameter or broad, with each frond tapering from the broader mid thallus towards the base and the apex, attached by a small discoid holdfast 100 µm–1 mm across which bears 1 to numerous erect fronds; epilithic or occasionally epiphytic on seagrasses. Structure polystichous, with a medulla 2–4(–6) cells broad, grading to the cortex 2–3 cells thick, outer cells small, isodiametric (toL/B2), 4–6(–8) µm across, each with a single phaeoplast and pyrenoid. Phaeophycean hairs single or usually in groups, profuse, becoming sunk in a pit, 5–8(–10) µm in diameter. Crustose stage discoid, ralfsioid, 2 mm–5 cm across and 60–100 µm thick when sterile, with radiating basal filaments, monostromatic at the margins, and erect filaments from most cells; cells of erect filaments 7–9 µm in diameter, L/B0.6–1.4;phaeophycean hairs in scattered groups, 5–6 µm in diameter.

Reproduction.The erect phase with sori of plurilocular organs, at first discrete and often pulvinate or elongate, extending over most of the surface, the zooidangia (20–) 30–40 µm and (6–)10–14 locules long, with 4–6 rows corresponding to each cortical cell, each row uniseriate with occasional divided locules, 2–3 µm in diameter; zooids mostly acting as mitospores and giving rise to erect, terete or compressed, thalli under winter (short day) conditions, and to crustose thalli in summer conditions, with the zooids acting as gametes (slightly anisogamous from dioecious thalli) between August and October. Paraphyses frequent amongst the plurilocular organs, simple (rarely divided into two), clavate, pyriform or shortly linear, (20–)30–40 µm long and 8–12(–15) µm in diameter, usually packed with physodes, extending to the surface or beyond the reproductive organs, remaining after the latter have been lost.Crustose stage with paraphyses (80–)100–140 µmand 8–12 cells long, slightly clavate with the apical cell 6–8 µmin diameter and L/B 1–1.5 (–2), bearing unilocular sporangia on a 2–3 celled lateral pedicel from a lower cell of the paraphysis; sporangia clavate to elongate-ovoid, 30–60 µmlong and (10–)20–25 µmin diameter.

Distribution.In southern Australia, from Cottesloe, W. Aust., to at least Sydney, N.S.W., and around Tas.

Habitat. Characteristic of the lower to mid eulittoral on rocks on rough-water to moderately sheltered coasts, with the erect stage rarely on seagrasses (Zostera and Posidonia). Scytosiphon lomentaria is common on intertidal rocks in winter, often as monospecific communities.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 294–295 (1987)]