Dasya divergens Parsons & Womersley

Scientific Description

Habit and structure. Thallus light grey-red to dark red, not mucilaginous and not adhering to paper on drying, 5–15(–20) cm high, spreading, with 1–3 corticated axes 1–2 mm in diameter bearing irregular patent laterals densely covered (except near the base) with tufts of branched pseudolaterals. Main axes bearing, irregularly radially, laterals of various lengths at intervals of 1–5 mm; axes 0.2–1 mm in diameter, 0.5–3 cm long, more-or-less linear, moderately heavily corticated from close to their apices, arising from the basal cell of the first branch of the pseudolaterals. Holdfast discoid, loosely rhizoidal, 0.5–1.5 cm across; epilithic. Structure. Pericentral cells 5, always clear in section but corticated outwardly by slenderer rhizoids. The first pericentral is cut off 5–6 segments from the apex, and by the time the fifth pericentral cell is formed (on segments 8 or 9) a secondary pit-connection is established via a small cell from the whole lower end of the pericentral cell; later secondary pit-connections arise via cells cut off from near the end of a pericentral cell. The first corticating rhizoids form from pericentral cells 17–20 segments from the apices, and descend over the pericentral cells. Pseudolaterals one per segment, 1–1.5 mm long, with 5–12 subdichotomies every 1(–2) cells from their base, of similar diameter until the ultimate branch of (2–)3–5(–8) cells which tapers to an acute point; branches divariate, rigid, lying at right angles at each branching; basal cells 50–70(–100) µm in diameter and L/D 0.5–1.5, mid cells (40–)45–70 µm in diameter and L/D (1–)2–3(–4). Adventitious monosiphonous filaments absent. Rhodoplasts discoid to elongate, becoming chained.

Reproduction. Gametophytes dioecious. Procarps borne successively and spirally on a polysiphonous lateral; the first sterile group initial is cut off from the fertile pericentral cell on the sixth segment, and by the ninth segment a mature procarp with a 4-celled carpogonial branch and two sterile group initials is present; after fertilisation, the sterile group initials each divide once. The auxiliary cell fuses with the central cell of the fertile segment via a new connection, and produces three primary gonimoblast initials, then a monopodial gonimoblast often branching unilaterally. Carposporophyte with a slight basal fusion cell, carposporangia ovoid to subspherical, 15–22 µm in diameter, in rows of 3–4(–5) often with 1(–2) lateral sporangia on the basal one. Cystocarps sessile on laterals or on short polysiphonous stalks, globose, 700–1100 µm in diameter with a neck 0.2–0.5 as long as the cystocarp diameter; pericarp 3–4 cells thick with outer cells ovoid to elongate, irregularly placed. Spermatangial branches as ultimate branches of pseudolaterals, lanceoid, 90–170 µm long and 30–40 µm in diameter, with a 1–2 celled pedicel and sterile apex 3–5 cells long, and 6–10 axial cells cutting off initials and an outer layer of spermatangia. Stichidia borne on the lower branches of pseudolaterals, on 1–3-celled monosiphonous stalks, cylindrical, 300–600 µm long and 120–150 µm in diameter, with (4–)7–20 fertile segments each with (5–)6 pericentral cells all of which become fertile, and with a short, mucronate, 2–3-celled apex. Tetrasporangia 25–35 µm in diameter, each with (2–)3 cover cells, initially small but at maturity covering most of the sporangium.

Distribution. 16 km E of Eucla, W. Aust., to Walkerville, Vic.

Habitat. D. divergens occurs from upper sublittoral pools to 20 m deep, fertile in summer to late autumn.

[After Parsons & Womersley in Womersley, Mar. Benthic Fl. Southern Australia IIIC: 450–452 (1998)]