Bornetia binderiana (Sond.) Zanardini

Scientific Description

Habit and structure. Thallus light to medium red, 3–9(–13) cm high, lax and flabellate, subdichotomously and mostly unilaterally branched at intervals of 1–2 cells, more distantly near the base. Attachment by an erect basal cell which in some plants produces short rhizoidal cells. Structure. Upper cells 500–900 µm in diameter and L/D 2–3, lower cells 600–700 µm in diameter and L/D 2–4. Cells multinucleate; rhodoplasts discoid.

Reproduction. Gametophytes dioecious. Female axis of 6–8 small cells borne on a larger basal cell containing crystalline inclusions, arising adaxially in the position of a lateral branch; involucral branches arising from the larger basal and lower 2 small cells of the fertile axis in a one quarter spiral pattern, unbranched or subdichotomously branched once; basal involucral cells oblong, radiating horizontally, bearing 1(–2) erect, elongate, incurved cells terminally, producing a basket-shaped condensed branch system; 2(–3) procarp systems produced successively from subapical cells in a one quarter spiral pattern, each consisting of 1(–2) periaxial sterile cell(s) often developing into 2-celled non-functional carpogonial branch(es), and a supporting cell bearing a lateral, recurved, 4-celled carpogonial branch and apically a sterile cell or a non-functional 2-celled carpogonial branch. Following fertilization in the first formed (lowest) procarp system, the supporting cell divides to form an auxiliary cell which is intercalated between the non-functional carpogonial branch and residual supporting cell and this divides forming 1–2 gonimolobes. Fusion cell stellate, 200–270 µm across, produced from the auxiliary cell and densely branched lower gonimoblast cells; carposporangia granular, ovoid-lachrimiform, 42–55 µm in diameter and L/D 1.6–2, with several vacuoles radiating from a single, central nucleus, borne at first on subdichotomous chains of cells, ultimately at the end of slender processes from the fusion cell. Spermatangial heads sessile, elongate, 130–140 µm in diameter and L/D 2.5–3, single (–2) and apical on 3(–5) small angular cells which branch laterally in a one quarter spiral pattern producing a further angular cell and 1(–3) large elongate, incurved involucral cells resulting in a basket-shaped, compressed branch system; heads not exceeding the length of the involucre. Tetrasporangia sessile, in clusters of 2–4, borne in comparable positions to spermatangial heads in similar condensed lateral branch systems with a one quarter spiral branching pattern, the terminal cells of which form incurved involucres; sporangia ovoid, 53–85 µm in diameter, tetrahedrally divided.

Distribution. Champion Bay, W. Aust., to Port Phillip, Vic.

Habitat. Usually epiphytic on red algae at moderate depths.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 314–315 (1998)]