Laurencia forsteri (Turner) Grev.

Scientific Description

Habit and structure. Thallus red to red-brown, moderately soft, 2–6(–8) cm high, slender, spreading with radial, terete branches at wide angles, mostly 2–5 mm apart; lower branches 0.5–1 mm in diameter, decreasing to 300–500 µm in branchlets. Holdfast flat, discoid, 1–3 mm across; epiphytic on Posidonia, occasionally Amphibolis. Structure. Epidermal cells near apices polygonal to slightly elongate, 15–20 µm across, enlarging below to 20–30(–50) µm broad and L/D 3–5(–8), with secondary pit-connections and corps en cerise; lenticular thickenings usually abundant in inner cortical cells. Cells uninucleate, multinucleate in larger cells; rhodoplasts discoid, chained in larger cells.

Reproduction. Gametophytes dioecious. Procarps not observed. Carposporophytes with a small basal fusion cell and short branched gonimoblast bearing clavate carposporangia 30–60 µm in diameter. Cystocarps sessile, globular and urceolate, with broad, slightly constricted bases, (300–)500–1100 µm in diameter; pericarp ostiolate, 2–3 cells thick, with a distinct neck 100–150 µm high. Spermatangial receptacles terminating clavate to pyriform branchlets, 300–700 µm across, spermatangia borne on trichoblasts. Tetrasporangia in simple or compound, clavate, branchlets 400–700 µm broad and 0.5–1(–2) mm long, in parallel arrangement and cut off abaxially, 120–220 µm in diameter.

Distribution.Houtman Abrolhos, W. Aust., to Wilsons Promontory, Vic., and N Tas.

Habitat. L. forsteri is a distinctive species, confined largely to the leaves of Posidonia (occasionally Amphibolis) in conditions of moderate water movement.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 459–462 (2003)]