Zonaria spiralis (J.Agardh) Papenf.

Scientific Description

Habit and structure. Thallus dark brown, 3–15(–22) cm long, much branched, with spirally twisted branches above, axes and lower branches complanate and stupose, 1–5(–9) mm broad, arising from a matted rhizoidal holdfast 3–10(–20) mm across and 5–10 mm long; epilithic. Fronds irregularly laterally branched with frequent short spinous laterals, regularly twisted, mostly spirally at least in their upper parts, 1–2(–3) mm broad throughout, with faint concentric growth or hair zones and often with darker central cells forming a slight midrib in surface view. Structure 8(–10) cells and (120–)160–200 µm thick throughout, with cells in regular rows in transverse section and cortical cells usually mostly (occasionally less than half) paired with (2–)3–4 cortical cells to each medullary cell lengthwise; cortical cells (when paired) 6–10 µmacross and L/B 1.5–2(–2.5). Hair tufts scattered or in concentric lines, hairs phaeophycean, 14–18 µmin diameter.

Reproduction. Sori with sporangia amongst paraphyses on upper branches, indusiate early then lost; sporangia ovoid to pyriform, 120–200 µmlong and 80–100 µmin diameter, with 8 spores, without a stalk cell; paraphyses 6–10 cells and 250–450 µm long, clavate with ovoid upper cells 25–40 µmin diameter. Oogonial sori scattered, round to irregularly ovate, 100–500(–1000) µmacross; oogonia clavate, with a stalk cell, 80–100 µmlong and 30–40 µm in diameter. Antheridial sori reddish brown, irregular in shape, mostly 0.5–2 mm long and 0.5–1 mm across.

Distribution.From Dongara, W. Aust., to Flinders, Vic.

Habitat. Z. spiralis is usually a moderately deep water (to 38 m) species, only occurring in shallow water when in heavy shade.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 250–252 (1987)]