Laurencia filiformis (C.Agardh) Mont.

Scientific Description

Habit and structure. Thallus medium to dark red, firm, drying cartilaginous, 6–15 cm high, to 30 cm in deep-water forms; f. filiformis slender, branches spreading, irregularly radial; f. heteroclada and f. dendritica with one to several main axes, radially and usually densely branched, pyramidal in form; lower axes terete, 600–800(–1000) µm in diameter in f. filiformis, 1.5–2 mm in f. heteroclada and 2–3 mm in diameter in f. dendritica, decreasing to upper branchlets 400–800(–1000) µm in diameter in f. filiformis, 800–1200 µm in f. heteroclada and f. dendritica. Holdfast discoid, 1–3 mm across in f. filiformis when epiphytic usually on Amphibolis; discoid, becoming stoloniferous, and 3–10 mm across in f. heteroclada and f. dendritica which are epilithic. Structure. Epidermal cells near apices isodiametric to slightly elongate, (15–)20–40(–50) µm across, L/D increasing to 2–3 below, with secondary pit-connections and corps en cerise; cortical cells with only small intercellular spaces, lenticular thickenings usually present (rare in f. dendritica). Cells with discoid to elongate rhodoplasts, chained in larger cells.

Reproduction. Gametophytes dioecious. Procarps not observed. Carposporophytes with a basal fusion cell and short, branched gonimoblast bearing clavate terminal carposporangia 30–80 µm in diameter. Cystocarps sessile, not or slightly basally constricted, ovoid to slightly conical, 600–1000(–1500) µm in diameter; pericarp broadly ostiolate, with or without a slight neck, 4–5 cells thick. Spermatangial receptacles ovoid to shortly clavate, becoming broad and cupulate, 0.8–1.5 mm across, spermatangia borne on trichoblasts. Tetrasporangia in simple to compound ramuli 1–2(–3) mm long and 400–800 µm in diameter, cut off abaxially in parallel arrangement, (70–)100–150 µm in diameter.

Distribution.Houtman Abrolhos, W. Aust., to Tilba, N.S.W., Qld (?), and around Tas. New Zealand (?). Recorded from Indian Ocean localities, from Brazil, and from the western tropical Atlantic (?).

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 469–473 (2003)]