Wilsonaea dictyuroides (J.Agardh) F.Schmitz

Scientific Description

Habit and structure. Thallus medium to dark red-brown, 4–25 cm high, much branched irregularly radially, with a robust main axis 2–3 mm in diameter and laterals 0.5–1.5 mm in diameter, denuded below the apical tufts of monosiphonous laterals at the ends of lesser branches. Holdfast discoid-conical, 2–10 mm across; epilithic. Structure. Apices monopodial, apical cells dome-shaped, 14–20 µm in diameter with thin walls, monosiphonous and unbranched for 8–12 cells and below this cutting off exogenous lateral monosiphonous branches from each of 4–6 cells, with segments below this cutting off 4(–5) pericentral cells bearing monosiphonous lateral filaments which become basally polysiphonous; pericentral cells dividing transversely into 2 irregular tiers and thus with 2 tiers between the monosiphonous lateral branches, and later becoming separated by rhizoidal cells and with a cortex becoming many cells thick below; the rhodoplastic monosiphonous laterals become branched at each cell in their lower parts, with adhering bases at the dichotomies, and the lower segments become polysiphonous; lower monosiphonous cells 50–75 µm in diameter and L/D (1–)1.5–2.5, upper simple branches 5–12 cells long, tapering to terminal cells 20–30 µm in diameter and L/D (2–)5–8, apices rounded. Cells uninucleate, larger ones multinucleate; rhodoplasts discoid, chained in larger cells.

Reproduction. Gametophytes dioecious. Procarps on special polysiphonous branches below terminal tufts, on several successive segments, with a 4-celled carpogonial branch. Carposporophytes with a basal branched fusion cell and branched gonimoblast with shortly clavate terminal carposporangia 30–45 µm in diameter; vegetative cells adjacent to the gonimoblast base becoming darkly staining. Cystocarps lateral and terminal on short branches, more-or-less ovoid, 0.3–1(–1.5) mm in diameter; pericarp ostiolate, with about 10 longitudinal filaments, corticated and 5–8 cells thick, outer cells isodiametric, irregularly placed. Spermatangia cover lower monosiphonous cells of the laterals, with short pericentral cells branching and lying along the parent cell and producing an outer cortical layer then with outermost spermatangial initials. Stichidia robust, borne near base of lesser branches, lanceoid to elongate, 250–450 µm in diameter and 1–1.5 mm long, with whorls of 4–5 pericentral cells and 3–4 tetrasporangia 70–120 µm in diameter, 3 cover cells and an outer layer of cortical cells.

Distribution.Hopetoun, W. Aust., to Western Port, Vic.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 489–492 (2003)]