Spongoclonium fasciculatum J.Agardh

Scientific Description

Habit and structure. Thallus erect, medium to dark red-brown, 10–30 cm high, irregularly branched with one to a few main axes and strongly developed main laterals, densely corticated in mid and lower parts but branches ecorticate for many cells below their apices. Holdfast rhizoidal, 5–12 mm across; epilithic or on Amphibolis. Structure. Axial cells 50–120 µm in diameter near apices, 130–250 µm in diameter below and L/D 2–7, longer basally within the cortication; each axial cell bearing a single, spirally arranged, ecorticate, basally branched, branchlet, often clustered or fasciculate but readily denuded in parts, tapering from 10–22(–30) µm in diameter basally, cells L/D 4–6, to 8–13 µm in diameter, cells L/D 4–5, near their apices; cortical rhizoids (10–)20–40 µm in diameter, cells L/D 4–6. Cells multinucleate; rhodoplasts discoid.

Reproduction. Gametophytes dioecious. Carpogonial branches 4-celled, borne on the subterminal cell of short, lateral, 3-celled branchlets, with the third cell bearing 2 sterile periaxial cells; the 3 sterile cells enlarge and become rounded. Following fertilization, the auxiliary cell produces successive, rounded, gonimolobes 130–350 µm across with carposporangia 10–20 µm in diameter, and a loose involucre of filaments develops from axial cells below the carposporophyte. Spermatangial heads are borne on cells of branchlets in the mid to upper thallus. Each head is sessile (without a stalk cell), 50–70(–90) µm long and 40–50 µm in diameter, with an axis of 6–8(–10) cells bearing whorls of cells and ultimate spermatangia 2–3 µm in diameter. Tetrasporangia occur on branchlets in the mid and upper thallus, sessile, subspherical to slightly ovoid, (20–)40–50 µm in diameter, tetrahedrally divided.

Distribution. Hopetoun, W. Aust., to Westernport Bay, Vic., and the N coast of Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 291–292 (1998)]