Placophora binderi (J.Agardh) J.Agardh

Scientific Description

Habit and structure. Thallus prostrate, flat, dark brown-red, 1–2 cm long and 3–6 mm broad, apex rounded, simple or branched, epiphytic on Codium, attached by rhizoids from the ventral pericentral cells. Structure. Margin of numerous apical cells terminating polysiphonous filaments laterally united in the broad thallus apex, without trichoblasts (apart from sexual plants). Apical cells squat, flat-topped, 10–16 µm broad and 10–12 µm long, axial cells cutting off 5 pericentral cells dorsiventrally, 3 dorsally and 2 ventrally; mature pericentral cells 15–25 µm in diameter and L/D (2–)3–5. Branching of the main axial cells in alternate pairs, in lateral axes one to several cells apart. Rhizoids cut off from the ventral pericentral cells, 20–30 µm in diameter, penetrating between the Codium utricles. Cells with discoid rhodoplasts.

Reproduction.Unknown in Australian material. Gametophytes dioecious; reproductive organs on short, free, polysiphonous branches bearing trichoblasts, on the thallus margins. Cystocarps ovoid, 180–250 µm in diameter (immature); pericarp ostiolate, ecorticate, 2 cells thick, outer cells isodiametric. Spermatangial organs on trichoblasts, clustered, ovoid-lanceoid, 90–150 µm long and 40–65 µm in diameter, with 3–4 sterile apical cells. Stichidia in small clusters, cylindrical, 180–360 µm long and 50–70 µm in diameter, with tetrasporangia in a straight row, one per segment, 30–50 µm in diameter, with 2 cover cells.

Distribution.Elliston, S. Aust. South Africa, Mozambique, Timor?. New Zealand.

Habitat. P. binderi is most commonly epiphytic on Codium.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 360–361 (2003)]