Erythroclonium angustatum Sond.

Scientific Description

Habit and structure. Thallus medium to dark red, 5–15 cm high, much branched with narrow, almost linear, constricted segments (3–)4–10 mm long, (250–)400–800 µm in diameter, with 2–5 branches from segment apices, lower branches only slightly thickened. Holdfast branched, with rhizoidal attachment pads; epiphytic on Amphibolis and Posidonia, occasionally epilithic. Structure uniaxial, with each axial cell producing two periaxial filaments diverging at about 90°, alternating on adjacent cells, forming a lax medulla with few rhizoids around the axial cells in young segments, old branches with moderately dense rhizoids in the medulla. Cortex pseudoparenchymatous, 2–3 cells thick, inner cells ovoid and 12–18 µm in diameter, outer cells 8–15 µm in diameter and L/D 1–2, only slight meristematic thickening of lower parts. Rhodoplasts discoid to elongate, numerous per cell.

Reproduction. Sexual reproduction non-procarpic. Carpogonial branches 3-celled, borne on outer medullary cells, directed inwards with reflexed trichogynes, rarely with a sterile cell on the basal cell. Connecting filaments 1(–3), non-septate apart from next to the carpogonium, usually unbranched. Auxiliary cell an outer medullary cell with adjacent cortical cells forming chains of small, darkly staining nutritive cells. Gonimoblast initial inwards, developing a prominent stalked fusion cell with radial gonimoblasts producing chains of ovoid carposporangia 30–50 µm in diameter. Cystocarps lying within the medulla, with filamentous enveloping tissue, slightly swelling the segments, ostiolate. Spermatangia unknown. Tetrasporangia scattered in the cortex of young segments, developed frominner cortical cells and pit-connected laterally, protruding into the medulla, ovoid, 50–70 µm long and 22–30 µm in diameter, zonately divided.

Distribution.Point Sinclair, S. Aust., to Phillip I., Vic.

Habitat. E. angustatum occurs mainly on the seagrasses Amphibolis and Posidonia.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 353–355 (1994)]