Antithamnionella ternifolia (Hook.f. & Harv.) Lyle

Scientific Description

Habit and structure. Thallus medium to dark red-brown, tufted (often dense), with prostrate axes bearing erect axes 4–40 mm high, each axial cell with (2–)3–4 whorl-branchlets. Lateral branches mostly every 3–4 axial cells, replacing whorl-branchlets or arising from lower cells of whorl-branchlets. Attachment of prostrate axes by single (–3) rhizoids from basal cells of whorl-branchlets, each with terminal digitate haptera; epiphytic on various algae, or on solid substrates. Structure. Apical cells 5–6 µm in diameter and L/D 1.5–2, initiating whorl-branchlets 3–7 cells from branch apices, axial cells increasing gradually to 30–75 µm in diameter and L/D 3–5(–8). Whorl-branchlets overlapping near apices, separated below, 200–300 µm and 10–15 cells long, simple or with 1 to a few simple branches which are often unilaterally arranged; cells of whorl-branchlets basally unbranched, 12–18 µm in diameter and L/D 1.4–1.8, decreasing gradually to tapering terminal cells 6–9 µm in diameter and L/D 1.5–2.5, with rounded ends; basal cell usually distinctly shorter than next cells; gland cells on lower to mid (commonly third or fourth) cells of whorl-branchlets, cut off from subterminal cells, touching only the bearing cell, ovoid, 8–11 µm in diameter. Cells uninucleate; rhodoplasts elongate in smaller cells, becoming ribbon like in axial cells.

Reproduction. Gametophytes usually monoecious. Carpogonial branches borne on the basal cells of short, 2-celled whorl-branchlets several cells below apices, with usually only one at each branch apex; no other whorl-branchlets occur on the fertile axial cell, and the terminal cell of the fertile branchlet is lost during carposporophyte development. Post-fertilization, fusion occurs between the carpogonium and auxiliary cell via a connecting cell, and a terminal gonimolobe develops from the central cell following division of the auxiliary cell, with the axial cell, residual supporting cell and foot cell fusing. A terminal and up to 6 lateral, ovoid to elongate, gonimolobes 90–120 µm across develop, with ovoid carposporangia 10–20 µm in diameter; no involucral branchlets develop. Spermatangia commonly occur on carposporophytic plants, with short adaxial clusters on cells of the rachides, the spermatangia cut off terminally. Tetrasporangia occur on the upper side of basal and often the second cells of several successive whorl-branchlets on upper branches, sessile, ovoid, 25–35 µm in diameter, subdecussately divided.

Distribution. From Shark Bay, W. Aust., and from Port Stanvac, S. Aust., to Westernport Bay, Vic., and N and E Tas., N.S.W.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 166–167 (1998)]