Sporochnus radiciformis (Turner) C.Agardh

Scientific Description

Habit and structure. Thallus medium brown, (10–)20–90 cm long, usually pyramidal in form with one (to several) main, percurrent axis bearing numerous long, radially arranged, laterals progressively decreasing in length towards the apex, each lateral similarly branched to 4 or 5 orders, each ultimate branchlet with an apical tuft of assimilatory filaments which is usually lost from older parts; holdfast rhizoidal, 2–15(–20) mm across and 4–15 mm long, with older main axes becoming stupose; epilithic. Growth apical, with a convex branch meristem surmounted by the tuft of trichothallic filaments 1–4(–6) mm long, each with a meristem 5–8 cells above their base, 12–25(–40) mm in diameter above with cells L/B 3–8. Fronds slender, becoming robust below, (0.5–)1–2 mm in diameter in lower axes in young plants, increasing to 2–3 mm in older plants by periclinal cortical divisions, 200–300 µmin diameter near the apices, with the branchlets (0.5–)1–3 mm apart, (0.5–)1–6 mm long and 60–100 µmin diameter. Structure haplostichous and pseudoparenchymatous with a medulla of elongate cells and a single-layered cortex (becoming multilayered in older axes) with cells 6–10 µmacross and L/B (1–)1.5–2.5.

Reproduction. Sporangial receptacles immediately below apical tufts, globular to pyriform or ovoid, becoming clavate in some specimens, (300–)400–1000 µm(–3mm) long and (150–)250–700 µmin diameter, with a sterile pedicel 1–2(–6) mm long and several times the length of the receptacle. Paraphyses 60–80 µmand 5–6 cells long, simple with the larger terminal cell pyriform to subspherical, (8–)10–16 µmin diameter, bearing lateral, clavate, unilocular sporangia 20–30 µm long and 6–8 µmin diameter. Gametophyte unknown.

Distribution. From Horrocks Beach,W. Aust., around southern Australia and Tas., to Botany Bay, N.S.W.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 284–285 (1987)]