Drewiana nitella (Harv.) Gordon-Mills

Scientific Description

Habit and structure. Thallus medium red to dark red-brown, 5–25 cm high, erect axes with distichous, alternate or opposite, branches, each axial cell with 4 or 5 whorl-branchlets. Holdfast 2–12 mm across, rhizoidal; epilithic. Structure. Subapical cells bearing 4 or 5 whorl-branchlets, overlapping only near branch apices, pinnately to subdichotomously branched 5–8 times, terminal cells acute, 18–24 µm in diameter and L/D 2.5–7; median cells 25–70 µm in diameter and L/D 2–6, basal cells 85–120 µm in diameter and L/D 1.5–2.5; axial cells 400–500 µm in diameter and L/D 4–6 below. Indeterminate branches arise on axial cells in position of whorl-branchlets. Cortication by rhizoids from basal cells of whorl-branchlets. Cells multinucleate; rhodoplasts discoid.

Reproduction. Gametophytes probably dioecious. Female axes 5–6 cells long, formed in position of a whorl-branchlet or a lateral thereof, the subapical cell bearing 3 pericentral cells, with one (the supporting cell) bearing a terminal sterile cell and a lateral carpogonial branch; the hypogenous cell is 2–3 times as long as the subapical cell. Post-fertilization 2 small connecting cells are formed each side of the carpogonium, and following fusion with the auxiliary cell the fusion cell produces a cluster of small gonimoblast cells, the lower ones fusing with each other, the auxiliary cell and the supporting cell, and the terminal ones forming clavate carposporangia 20–25 µm in diameter; carposporophyte 240–500 µm across. The apical cell of the fertile axis, the 2 pericentral cells and the sterile cell on the supporting cell divide to form 4 inner involucral groups around the carposporophyte. Spermatangia unknown. Tetrasporangia are borne terminally or laterally on the adaxial sides of lower cells of whorl-branchlets, 25–50 µm in diameter, tetrahedrally divided.

Distribution. Houtman Abrolhos, W. Aust., to Port Phillip Heads, Vic., and E Tas.

Habitat. D. nitella is a deep-water species.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 78–79 (1998)]