Wrangelia velutina (Sond.) Harv.

Scientific Description

Habit and structure. Thallus medium to dark brown-red, 3–16 cm high, irregularly branched for 2–3 orders, branches terete, 1–2 mm in diameter, diverging widely, usually widely spaced, often unequal in length. Holdfast 3–7 mm across, rhizoidal; epilithic (as short plants 3–6 cm high) or epiphytic on Amphibolis (larger, deeper water plants). Structure. Axes with small apical and sub-apical cells, enlarging to 200–300 µm in diameter and 400–500 µm long near the base. Each axial cell with 5 whorl-branchlets, developed from periaxial cells with the first formed often produced unilaterally, the first 3 in sequence around the axial cell, the fourth and fifth alternating. Mature whorl-branchlets 1–1.5 mm long, subdichotomous 7–8 times, ultimate parts 2–4 cells long, terminal cells mucronate and L/D 1–2, median cells (40–)55–90 µm in diameter and L/D 2–6. Indeterminate laterals arising on basal cell of whorl-branchlets, cortex 0.5–1 mm thick below. Cortication by descending rhizoids (often spiral) from the basal cells of whorl-branchlets, cortex 0.5–1 mm thick below. Cells uninucleate; rhodoplasts discoid, in chains in larger cells.

Reproduction. Gametophytes dioecious. Procarps formed on sub-apical cells as in W. plumosa, the supporting cell without a sterile cell. Post fertilization development as in W. plumosa, with the carposporophyte intermixed with sterile whorl-branchlets, the whole 700–1000 mm across; carposporangia clavate, 25–40 µm in diameter; axial cells below the fusion cell swelling and pit-connections enlarging. Spermatangial heads developed as in W. plumosa, 45–125 µm in diameter. Tetrasporangia borne as in W. plumosa, each surrounded by 1–2 small-celled involucral branchlets from the stalk cell, sporangia 45–90 µm in diameter, tetrahedrally divided.

Distribution. Rottnest I., W. Aust., to Western Port, Vic.

Habitat. Small plants of W. velutina occur just above or below low tide level on rough-water coasts, while larger plants are epiphytic on Amphibolis in deeper, less turbulent water.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 28–31 (1998)]