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Polysiphonia isogona Harv.

This name is not current. Find out more information on related names.

Reference
Fl.Nov.-Zel. 231 (1855)
Conservation Code
Not threatened
Naturalised Status
Native to Western Australia
Name Status
Not Current

Scientific Description

Habit and structure. Thallus medium to dark red-brown, (1–)3–15(–20) cm high, forming densely and irregularly branched, lax, often fastigiate tufts with numerous axes (often partly denuded below) arising from prostrate, entangled filaments. Attachment by rhizoids from prostrate filaments; usually epilithic. Structure. Prostrate filaments (100–)140–250 µmin diameter with segments L/D 0.5–1.2(–3), with scattered unicellular rhizoids cut off from the proximal ends of pericentral cells; erect branches 125–250(–300) µmin diameter with segments L/D (0.8–)2–4, extending to L/D 6 in mid parts of long axes, decreasing gradually to 30–80 µmin diameter with segments L/D 0.7–1 near the straight apices with moderately prominent trichoblasts which are lost below the upper few segments; lateral branches arising from the side of the basal cell of trichoblasts, the latter usually soon lost; cicatrigenous branches usually absent. Pericentral cells (8–)9–10, rarely 7, elongate throughout the thallus, ecorticate; trichoblasts or scar cells variable in position, from occasional on lower branches to every 2–4 segments above or sometimes on every segment with a divergence of one quarter or one fifth, trichoblasts relatively slender and short, 1–3 times furcate, basal cells 12–20 µmin diameter. Rhodoplasts discoid, usually densely aggregated, occasionally in chains.

Reproduction. Gametophytes dioecious. Carposporophytes with a slight basal fusion cell and short gonimoblast bearing clavate terminal carposporangia 25–45 µm in diameter. Cystocarps stalked, subspherical or slightly conical to ovoid, (200–)250–400(–600) µm in diameter; pericarp ostiolate, 2 cells thick, outer cells angular, isodiametric, ostiolar cells not enlarged. Spermatangial branches developing as one branch of a trichoblast, cylindrical, 150–220(–310) µm long and 25–60 µm in diameter, commonly with 1–3(–5) sterile apical cells when mature. Tetrasporangia forming long, gently spiralling series in upper branches with a divergence of one ninth, often extending below 1–3 laterals, slightly and evenly swelling the segments, occupying 0.5–0.8 the segment diameter when mature, subspherical to ovoid, 55–90 µm in diameter.

Distribution. New Zealand (widely distributed). In southern Australia from King George Sound, W. Aust., to Tas and Port Jackson, N.S.W.

Habitat. P. isogona usually grows as a turf, often amongst sand, at about low tide level under moderate to strong wave action, occasionally in calmer water.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 211–213 (2003)]