Antithamnion armatum (J.Agardh) G.De Toni

Scientific Description

Habit and structure. Thallus medium red-brown, with prostrate branched axes bearing erect unattached, distichously branched, fronds 1–3 cm high, the axial cells bearing opposite, distichously arranged pinnae with single pinnules on the upper side of each cell, just overlapping the pinna above. Attachment by rhizoids from the basal (and second) cell of the pinnae, each 3–7 cells long with a digitate hapteron; epiphytic on various algae. Structure. Apical cells 6–10(–15) µm in diameter and L/D 1–1.25, enlarging rapidly after a few cells, and to 130–300 µm in diameter and L/D 1–1.5(–2) in mature axial cells. Pinnae 500–800 µm and 8–12 cells long, closely branched, rachis cells 50–90 µm in diameter and L/D 1–1.4, slightly shorter basally and tapering to a small mucronate cell, each cell bearing a single pinnule (longest centrally on the pinna) adaxially, unbranched apart from adaxial short branches often bearing gland cells or tetrasporangia; pinnule cells 35–50 µm in diameter and L/D 1–1.5, tapering above to small, mucronate terminal cells; gland cells frequent, on short 2–3-celled branches, often on 2–4 successive cells near the base of the pinnules. Lateral branches arise near apices in place of pinnae. Cells uninucleate; rhodoplasts discoid to elongate, ribbon like in larger cells.

Reproduction. Gametophytes dioecious. Procarps borne in series of 4–8 on basal cells of pinnae at branch apices, with 4-celled carpogonial branches. Carposporophytes with 1–3 lobes, each 180–350 µm across, with ovoid carposporangia 25–45 µm in diameter. Spermatangia terminal on densely branched clusters on the end of the short branches bearing gland cells. Tetrasporangia borne on the lower side of special short branches which also bear the gland cells, sessile, ovoid, 45–75 µm in diameter, decussately or cruciately divided.

Distribution. Shark Bay, W. Aust., to Stinky Bay, Nora Creina, S. Aust.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 104–105 (1998)]