Thuretia quercifolia Decne.

Scientific Description

Habit and structure. Thallus medium to dark red, erect to decumbent, 10–25 cm high, complanately and laterally branched with flat branches mostly 1–2.5 cm broad and 0.5–1 mm thick, with polysiphonous axes bearing a network of monosiphonous filaments with surface unbranched filaments becoming spine-like on the margins, denuded below with slender axes. Holdfast conical, rhizoidal, 1–3 mm across, spreading by stolons. Structure. Apices sympodial, forming alternately distichous pseudolaterals which develop into determinate sympodial laterals forming the flat branches. Pericentral cells 4, formed in alternating sequence. Pseudolaterals occur alternately on each cell of the determinate laterals, and the monosiphonous network develops by branchlets becoming linked by small lateral cells, with free curved filaments on the surface of the network, more spine like on the thallus margin. Inner cells 25–55 µm in diameter and L/D 0.6–2, cells of free surface filaments 15–40 µm in diameter and L/D 1–3, when spine like, cells 50–150 µm in diameter and L/D 0.5–1. Mature axes become corticated by filaments arising from the pericentral cells which are no longer recognisable in older axes. Lateral axes arise from pseudolaterals near the apices. Rhodoplasts discoid in smaller cells, becoming chained or ribbon like in larger cells.

Reproduction. Gametophytes dioecious. Procarps occur on basal branches on determinate sympodia, with 5 pericentral cells, the fourth of which forms a sterile group and a carpogonial branch; the supporting cell forms a second sterile group. Post-fertilization a fusion cell develops from the auxiliary cell and central cell of the fertile segment and involves also the other pericentral cells and lower gonimoblast cells; the sterile groups divide extensively. The gonimoblast is much branched with terminal clavate carposporangia 25–35 µm in diameter. Cystocarps lie within the filamentous network, ovoid, on a short corticate stalk, 1–2 mm in diameter, corticated, with a prominent neck 0.7–1.2 mm long protruding through the network; the pericarp arises pre-fertilisation by division of the sterile pericentral cells, with the erect filaments becoming 5–6 layered with small outer cortical cells. Spermatangial branches are terminal on short filaments within the network, subglobose and 70–150 µm in diameter, with 3–4 axial cells each cutting off 4 pericentral cells which divide irregularly to form initials which each form 3–4 spermatangia. Stichidia occur in 2 rows on polysiphonous axes of determinate symposial laterals, formed on 4–6 cells of a monosiphonous network filament, ovoid and 150–200 µm in diameter, each with 6 pericentral cells and ovoid tetrasporangia (40–55 µm in diameter) plus 2–3 pre-sporangial cover cells.

Distribution. Dongara, W. Aust., to Walkerville, Vic., and N Tas.

Habitat.T. quercifolia is a common and distinctive species on southern rough-water coasts, usually occurring in deeper water.

[After Parsons & Womersley in Womersley, Mar. Benthic Fl. Southern Australia IIIC: 502–506 (1998)]