Heterocladia caudata L.E.Phillips, H.G.Choi, G.W.Saunders & Kraft

Scientific Description

Habit and structure. Thallus dark red-brown, erect, 20–60 cm high, with a terete to slightly compressed main axis bearing a few similar main lateral branches 5–20 cm long, all bearing a dense cover of terete, determinate, simple or occasionally branched, laterals 0.5–1.5 cm long and 300–500 µm in diameter, some bearing trichoblasts; axes denuded below, cartilaginous, 2–5 mm in diameter. Holdfast discoid with fibrous outgrowths, 2–10 mm across; epilithic. Structure. Apices tapering, apical cell dome-shaped, thick walled, axial cells cutting off 4 pericentral cells, rapidly corticated and producing abundant rhizoidal filaments from inner cells obscuring the pericentral cells; older axes have a medulla largely of entangled rhizoids with a thin outer cortex of small cells. Trichoblasts are produced apically from each segment, 300–900 µm long, below branched 2 cells apart with adherent walls at the branchings, lower cells 35–70 µm in diameter and L/D mostly 1–1.5, rhodoplastic. Cells uni- or multinucleate; rhodoplasts discoid to elongate.

Reproduction. Procarps usually on the second cell of trichoblasts, with the supporting cell bearing a 4-celled carpogonial branch and a sterile group of 3 cells. Carposporophytes with a basal fusion cell and a short, branched, gonimoblast with clavate terminal carposporangia 50–150 µm in diameter. Cystocarps stalked or subsessile, ovoid, 800–1200 µm in diameter; pericarp ostiolate, corticated, 4–5 cells thick. Spermatangia unknown. Tetrasporangia borne in simple or branched, corticated, determinate laterals bearing trichoblasts, spirally arranged, single per tier, 120–250 µm in diameter.

Distribution. Geraldton to Hopetoun, W. Aust.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 284–286 (2003)]