Liagora harveyana Zeh

Scientific Description

Habit and structure. Thallus (gametophyte) brownish red with a whitish crust, especially on lower parts, fairly strongly calcified (mainly in the inner cortex) but not rigid, 3–9(–14) cm high with one to several axes, dichotomously branched every 2–4(–8) mm, forming a dense rounded tuft; branches terete to slightly compressed; occasionally small proliferations may occur near the base, possibly following damage to the thallus; lower branches 1–2 mm in diameter, tapering gradually to 0.2–0.5 mm below apices. Holdfast discoid, 1–5 mm across; epilithic or on Amphibolis stems. Structure of a medulla of straight, moderately stout filaments 15–20(–50) µm in diameter, with relatively few rhizoids from the outer medullary cells or occasionally from innermost cortical cells, and a cortex 120–200(–300) µm broad, of branch systems usually 6–8 cells long, dichotomously branched usually at every cell, often trichotomous above; cortical cells (3–)5–10(–15) µm in diameter, elongate below, ovoid-moniliform, L/D 1.5–3 above, with smaller ovoid terminal cells; rhodoplasts more-or-less stellate with a central pyrenoid; hairs often common. Tetrasporophyte minute, largely prostrate, filamentous, irregularly branched.

Reproduction. Sexual thalli dioecious or occasionally monoecious. Carpogonial branches borne laterally on inner cells of cortical filaments, usually curved, of 4 (occasionally 3 or 5) cells with a conical carpogonium. Zygote dividing transversely once or twice, the upper cell segmenting obliquely to form rather erect, branched, gonimoblast filaments. Carposporophyte hemispherical, just within or when mature protruding slightly from the cortex, 200–350 µm across in surface view; carposporangia ovoid, (10–)15–30(–36) µm long by (6–)8–15 µm in diameter, when mature often divided horizontally or irregularly cruciately, with new carposporangia developing laterally from below, sometimes giving a group of 4 or 5 at the apex of each gonimoblast filament. Following fertilization the pit-connections of the carpogonial branch enlarge, and ultimately a fusion cell involving the carpogonial branch and lowest gonimoblast cells is formed. Sterile post-fertilization filaments develop from cortical cells above and below the supporting cell, sometimes from the supporting cell, forming a loose tangle around the carpogonial branch. These later produce numerous erect filaments, which closely resemble the cortical filaments and form an involucre around the carposporophyte; involucre conspicuous when young, less so when mature. Spermatangia produced at apex of cortical filaments in a digitate arrangement; spermatangia ovoid to spherical, 2–3 µm in diameter, cut off from elongate spermatangial initials borne polychotomously on the end cortical cells. Tetrasporophytes forming monosporangia or cruciately divided tetrasporangia.

Distribution.Nanarup, W. Aust., to Walkerville, Vic., and the N coast of Tas. New Zealand.

Habitat. L. harveyana is a common species in shallow water on rough-water rock platforms and occasionally on Amphibolis in deeper water.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 96–98 (1994)]