Wrangelia abietina Harv.

Scientific Description

Habit and structure. Thallus medium to dark red-brown, fading to grey-red, 10–30(–60) cm high, alternately pinnately branched for 3–4 orders, lateral branches 1–20 cm long. Holdfast 1–4 mm across, rhizoidal; epilithic or epiphytic on Codium. Structure. Apical and subapical cells small, dividing slightly obliquely and enlarging gradually to 400–700(–900) µm in diameter and 2–3 mm long near the thallus base. Each axial cell with 5 whorl-branchlets, developed form periaxial cells usually cut off in alternating sequence, the first on alternate sides on successive axial cells. Mature whorl-branchlets 1–2 mm long, overlapping, basally branched subdichotomously, ultimate (6–)8–10 cells unbranched, tapering, mid cells (18–)20–35(–45) µm in diameter and L/D 4–7. Indeterminate lateral branches arise from basal cells of whorl-branchlets, forming a pseudoparenchymatous cortex of longitudinal filaments, 1–8 mm thick below and exposed between the whorl-branchlets. Cells uninucleate; rhodoplasts discoid to elongate, ribbon like in larger cells.

Reproduction. Gametophytes dioecious. Procarps formed successively on the third to sixth axial cells of indeterminate apices, the supporting cell bearing a terminal sterile cell and a lateral 4-celled carpogonial branch. Post-fertilization two connecting cells are cut off from the carpogonium, and occasionally similar cells from lower carpogonial branch cells; one fuses with the auxiliary cell which produces 1–3 short gonimoblast filaments with the terminal cells becoming pyriform to clavate carposporangia 45–65 µm in diameter, with further carposporangia formed by lower cells. Lower gonimoblast cells gradually fuse and the carposporophyte becomes intermixed with sterile whorl-branchlets (with smaller cells than in normal whorl-branchlets), the whole forming a compact hemispherical mass 600–800 µm across. Spermatangia are formed terminally on radiating filaments of subspherical heads 40–60 µm in diameter, borne on the lower 1 or 2 cells of whorl-branchlets, surrounded by curved involucral branchlets. Tetrasporangia occur on the lower 1–3 cells of unmodified whorl-branchlets, subspherical, 80–100 µm in diameter, tetrahedrally divided.

Distribution. Yanchep, W. Aust., to Phillip I., Vic.

Habitat. W. abietinaappears to be a deeper water alga, commonly epiphytic on Codium galeatum on rough-water coasts.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 24–27 (1998)]