Colacodasya australica Womersley

Scientific Description

Habit and structure. Thallus light red-brown, pulvinate to globose, 2–4 mm across, with a central pseudoparenchymatous tissue and short, peripheral, free polysiphonous branches. Attachment by rhizoids penetrating between host cells; epiphytic on axes of Dasya clavigera. Structure. Central tissue of irregularly branched filaments linked laterally by secondary pit-connections, cells elongate to ovoid, inner cells 40–90 µm in diameter, outer cells 25–40 µm in diameter; attachment rhizoids penetrating between host cells, 15–25 µm in diameter with cells L/D 2–4, cells later becoming irregular and 30–60 µm across. Peripheral free filaments becoming polysiphonous with 5 pericentral cells, 70–170 µm in diameter with segments L/D 0.8–1.5, ecorticate but with ovoid cells 12–25 µm in diameter cut off from both ends of the pericentral cells. Apices probably sympodial, with pseudolaterals borne radially from each segment and branched from each (occasionally second) cell, upper filaments unbranched and 5–10 cells long. Pseudolaterals with lower cells 20–45(–60) µm in diameter and L/D 1–2.5(–4), tapering to apical cells (often lost) 12–22 µm in diameter, subapical cells L/D (1–)2–4, apical cell short. Rhodoplasts discoid, pale in colour.

Reproduction. Gametophytes monoecious. Procarps borne on basal cells of pseudolaterals which cut off 5 pericentral cells, with a 4-celled carpogonial branch and associated sterile cells. Cystocarps ovoid, broad based, 200–450 µm in diameter with a slight broad neck and borne laterally on a polysiphonous branch; gonimoblast much branched, with basal cells scarcely fusing, carposporangia in short terminal chains, ovoid, 7–15 µm in diameter. Pericarp with 12–14 erect filaments, 3 cells thick with ovoid, irregularly shaped and placed outer cortical cells 12–25 µm in diameter. Spermatangial branches on the same thallus as cystocarps, developed as single or paired terminal branches of pseudolaterals, 75–150 µm long and 25–35 µm in diameter, with or without a terminal row of sterile cells.Tetrasporangial stichidia lanceoid to cylindrical, 100–400 µm long and 50–70 µm in diameter, borne as branches of pseudolaterals on a monosiphonous base, with 5 pericentral cells and tetrasporangia per whorl, tetrasporangia 15–25 µm in diameter, each with 2 (undivided) ovoid cover cells which remain more-or-less erect and cover the lower half of the sporangia.

Distribution. Hopetoun, W. Aust., to Port MacDonnell, S. Aust.

Habitat. C. australica is often common on Dasya clavigera and is to be expected anywhere the host occurs.

[After Parsons & Womersley in Womersley, Mar. Benthic Fl. Southern Australia IIIC: 508–510 (1998)]