Polysiphonia amphibolis Womersley

Scientific Description

Habit and structure. Thallus dark brown-red, forming intricate tufts or a felt, usually not more than 1 cm high but occasionally with branches extending from the felt and up to 2 cm high. Attachment by rhizoids from prostrate filaments; epiphytic on the stems of Amphibolis, occasionally on Corallina or Chiracanthia. Structure. Prostrate filaments 70–120(–160) µm in diameter, tapering gradually to the pointed apices, with segments L/D 0.8–1.5, attached by scattered rhizoids cut off from the pericentral cells and with relatively massive multicellular haptera; axes branching irregularly spirally every (1–)2–5 segments, producing laterals cicatrigenously and with occasional simple or once branched trichoblasts or single trichoblast cells or scar cells present on every segment. Lateral branches (from prostrate axes) more or less erect, mostly 50–130 µm in diameter with segments L/D (0.8–)1.5–2.5(–3), tapering gradually to pointed apices, irregularly spirally branched every 1 or 2 segments with branches replacing trichoblasts and developed to varying extents, with many remaining simple. Pericentral cells 4, ecorticate; trichoblasts and scar cell generally present on every segment of erect branches, trichoblasts on well developed apices several times furcate, basal cells 20–30 µm in diameter. Rhodoplasts discoid or commonly ribbon-shaped, irregular or often orientated transversely in the pericentral cells.

Reproduction. Gametophytes dioecious. Carposporophytes with a slight fusion cell and short, branched gonimoblasts with clavate terminal carposporangia 20–25 µm in diameter. Cystocarps short-stalked, ovoid and orientated parallel to parent branch, becoming slightly urceolate when mature, 250–500 µm in diameter; pericarp ostiolate, 2 cells thick, outer cells isodiametric. Spermatangial branches replacing the whole trichoblast, 70–90 µm long and 35–60 µm in diameter, apically pointed, with a 1–2-celled sterile base and usually a small, sterile apical cell. Tetrasporangia forming a slightly spiral, short series (3–8) in the lesser branches, markedly swelling the segments above the sterile basal ones, 45–70 µm in diameter.

Distribution.Shark Bay, W. Aust., to Marino, Gulf St Vincent, S. Aust.

Habitat. Occurs mainly on Amphibolis; also recorded on Corallina and Chiracanthia.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 181–183 (2003)]