Wollastoniella myriophylloides (Harv.) Gordon-Mills

Scientific Description

Habit and structure. Thallus dark red-brown, fading to grey, 10–15(–20) cm high, main branches irregularly alternate, often sparse and divergent, for 2–4 orders. Base of axes often prostrate and entwined, forming a matted holdfast attached by haptera; usually epiphytic on Amphibolis,fucoids or geniculate coralline algae. Structure. Subapical cells producing 3–4 whorl-branchlets in circular sequence, axial cells enlarging to 300–350 µm in diameter and 2–3.5 mm long in lower axes; primary axes of whorl-branchlets 4 cells long, terminal cells maturing first and lower laterals produced basipetally; terminal cells short and mucronate, median cells 120–200 µm in diameter and L/D 3–5. Adjacent whorls of whorl-branchlets become separated with 0.5–2.5 mm of the axial cell exposed between them. Indeterminate branches (up to 4 from each axial cell) produced in addition to whorl-branchlets. Cortication by rhizoids from lower axes, produced from lower ends of axial cells, forming haptera from the proximal ends of the rhizoidal cells. Cells multinucleate; rhodoplasts discoid.

Reproduction. Gametophytes dioecious. Female axes 5–6 cells long, up to 4 such axes alternating with whorl-branchlets on potentially indeterminate branches, with the last 4 cells relatively small and densely protoplasmic. The subapical cell bears 2 sterile pericentral cells and the supporting cell which bears a terminal sterile cell and a lateral carpogonial branch; the hypogenous and subhypogenous cells are without laterals. Post-fertilization, 2 connecting cells are formed and the auxiliary cell produces gonimoblast initials which divide and form clavate carposporangia 60–100 µm in diameter; carposporophyte 450–1100 µm across; lower gonimoblast cells and sterile procarp cells fuse to form a relatively large multinucleate fusion cell, and the apical cell, the 2 sterile pericentral cells and the sterile cell on the supporting cell divide to form 4 inner involucral filaments. Spermatangial heads are subspherical, 90–110 µm in diameter, sessile and adaxial on cells of villose whorl-branchlets. Tetrasporangia occur terminally and laterally on small cells of much branched whorl-branchlets, borne just below the apex of short indeterminate branches; tetrasporangia are 100–160 µm in diameter, tetrahedrally divided (rarely octosporangia).

Distribution.Port Denison, W. Aust., to Port Phillip, Vic.

Habitat. W. myriophylloides is a moderately deep water alga, usually epiphytic on Amphibolis or larger algae.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 81–83 (1998)]