Herposiphonia calothrix (Harv.) Womersley

Scientific Description

Habit and structure. Thallus forming low mats, with extensive prostrate axes bearing simple, erect, 1–2 mm high, determinate laterals on 3 consecutive segments, separated by short indeterminate laterals, some developing into lateral axes adherent to the substrate. Attachment by rhizoids; epilithic or epiphytic on Corallina and Codium. Structure. Apices of indeterminate axes dorsally revolute, apical cells hemispherical, 10–15 µm in diameter. Axes 100–220(–250) µm in diameter, segments L/D 0.6–1(–2), with 8–9(–12) pericentral cells; determinate laterals arising dorsally, 70–100 µm in diameter, segments L/D (0.6–)1–2, with 7–8(–9) pericentral cells. Trichoblasts near ends of determinate laterals, 0.5–1 mm long, much branched, lower cells 12–18 µm in diameter. Rhizoids cut off from ventral pericentral cells, unicellular with digitate haptera (branch ends often cut off as separate cells). Cells multinucleate; rhodoplasts discoid to elongate, then often in parallel stacks.

Reproduction. Gametophytes dioecious. Procarps with a 4-celled carpogonial branch. Cystocarps (juvenile) ovoid; pericarp arising prefertilization, 2 cells thick with small corticating cells. Spermatangial organs replacing trichoblasts on mid to upper parts of determinate laterals, lanceoid, 100–550 µm long and 50–120 µm in diameter, with a sterile basal cell and terminal row of 2–5 sterile cells. Tetrasporangia in straight series in determinate laterals, one per segment, 50–75 µm in diameter, with 2–3 cover cells.

Distribution.Dirk Hartog I. and Sorrento, W. Aust., to Encounter Bay, S. Aust. Botany Bay and Long Reef, N.S.W.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 290–292 (2003)]