Botryocladia sonderi P.C.Silva

Scientific Description

Habit and structure. Thallus dark red-brown, 10–30 cm high, rigid and cartilaginous, with sparsely and irregularly branched, solid, terete, main branches 1–1.5 mm in diameter, bearing radially ovoid to obovoid, hollow, membranous, vesicular laterals 5–20(–25) mm long and 3–10(–14) mm in diameter, usually closely adjacent and each with a short, narrow, stipe, lost from lower axes with the stipe remnant remaining. Holdfast discoid, 2–10 mm across; epilithic. Structure multiaxial, branches solid with a small-celled cortex 3–6 cells thick, outer cells ovoid, 4–8 µm in diameter, grading to a larger-celled medulla, cells 40–80 µm in diameter and L/D 1–3 in longitudinal section, with frequent secondary pit-connections. Vesicular laterals with a continuous cortex 2–3 cells thick, outer cells ovoid, 4–10 µm in diameter, grading rapidly to a medulla 2–3 cells thick, the inner cells rounded, 40–65 µm across, lengthwise L/D 1–3, these larger cells cutting off smaller inner cells over their joint walls forming rosettes which become 3–5 cells broad. Secretory cells scattered, sparse, on inner larger medullary cells, single or in groups of 2–4(–9), subspherical, 30–40 µm in diameter, with a thick gelatinous wall. Rhodoplasts discoid.

Reproduction. Gametangial thalli probably dioecious. Carpogonial branches and auxiliary cell branches unknown. Carposporophyte with an erect, basal, fusion cell producing dense, compact, lobes of carposporangia 8–12 µm in diameter. Basal nutritive tissue broad and shallowly concave, erect filaments (which disintegrate) continuing to anticlinal pericarpic filaments. Cystocarps 0.8–1.3 mm across, protruding both outwardly and into the vesicle, with an outer pericarp 150–250 µm and 10–12 cells thick, ostiolate. Spermatangia unknown. Tetrasporangia in shallow nemathecia over the vesicles, the sporangia lying among elongate outer cortical cells (L/D 2–6), basally pit-connected to inner cortical cells and with slight pit-connections to the outer cells, ovoid, 25–45 µm long and 15–25 µm in diameter, decussately or cruciately divided.

Distribution.Port Denison, W. Aust., to N Waratah Bay, Vic., and the N coast of Tas.

Habitat. B. sonderi is a common species, from rough-water situations to calm areas with a strong current flow, and from low tide level to 24 m deep.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 48–49 (1996)]