Laurencia arbuscula Sond.

Scientific Description

Habit and structure.Thallus dark red-brown to red, firm, cartilaginous, 5–15 cm high, with one to several long axes developing long laterals, radially branched and usually pyramidal; all branches terete, with abundant short ramuli throughout, main axes (0.5–)0.7–1.5 mm in diameter, decreasing to 0.7–1 mm in lateral branches and to 300–500(–800) µm in diameter in the short ramuli. Holdfast discoid, with numerous axes, 2–5 mm across; epilithic. Structure. Epidermal cells compact, isodiametric and (15–)20–35 µm across; in surface view, elongating slightly below to L/D 1.5–2(–3), with secondary pit-connections and corps en cerise; inner cortical cells compact, without lenticular thickenings. Cells with discoid rhodoplasts, chained in larger cells.

Reproduction. Gametophytes dioecious. Procarps not observed. Carposporophytes with a basal fusion cell and short branched gonimoblast with clavate terminal carposporangia 30–55 µm in diameter. Cystocarps on short stalks or subsessile, broad-based, ovoid-conical, 600–1000 µm in diameter; pericarp ostiolate, with no or a slight neck. Spermatangial receptacles in summit of shortly clavate ramuli 500–900 µm across, spermatangia borne on trichoblasts. Tetrasporangia in short, branched, often fastigiate, clusters of ramuli, each 300–600(–800) µm in diameter and (0.5–)3–4 mm long, cut off abaxially in parallel arrangement, 80–130 µm in diameter.

Distribution.Rottnest I.,W. Aust., to Walkerville, Vic., and N Tas. Subtropical western Atlantic. Brazil.

Habitat. L. arbuscula grows near to low tide level on somewhat sheltered coasts.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 466–468 (2003)]