Polysiphonia daveyae Reinbold

Scientific Description

Habit and Structure. Thallus brown-red, 3–16 cm high with a single, erect basal axis, profusely irregularly branched on all sides with generally patent branching, more fastigiate above. Attachment by numerous unicellular rhizoids cut off from pericentral and cortical cells, often aggregated to form a discoid holdfast; usually epiphytic (on Posidonia, Codium galeatum and other algae). Structure. Lower main axes 1–2 mm in diameter, moderately to heavily corticated, decreasing to 500–800 µm in diameter with segments L/D 0.3–0.5(–0.8) in mid branches which are slightly to moderately corticated, then to 150–250 µm in diameter with segments L/D 0.3–0.8(–1) in not or scarcely corticated branches, with ultimate branchlets 50–75 µm in diameter with mature segments L/D 0.5–1, and tapering evenly and markedly to a slender, erect apex; trichoblasts usually soon lost, branches arising from the basal cell of trichoblasts and often cicatrigenously from older branches. Pericentral cells 4, more or less isodiametric in surface view throughout the thallus but often 1.5–2 times as long as broad near the apices, becoming corticated from their corners and cortication of short cells spreading around the pericentral cells as seen in surface view, becoming complete in older branches and several layers thick on old axes; trichoblasts (or scar cells) present on every segment with a divergence of one quarter, relatively slender (basal cells 20–25 µm in diameter), 2–4 times furcate. Rhodoplasts discoid and usually in chains.

Reproduction. Gametophytes dioecious. Carposporophytes with a small basal fusion cell and short gonimoblast bearing clavate terminal carposporangia 25–45 µm in diameter. Cystocarps short-stalked, subspherical to ovoid, non-urceolate, 300–500 µm in diameter; pericarp ostiolate, 2 cells thick, outer cells angular, isodiametric. Spermatangial branches developing as one branch of a trichoblast, cylindrical, 160–250 µm long and 50–80 µm in diameter, without a sterile apical cell when mature. Tetrasporangia forming gently spiral series in single branchlets, occasionally with a small lateral above, not or slightly bulging the segments and occupying about half the branch width when mature, subspherical to ovoid, 50–90 µm in diameter.

Distribution.Frenchmans Bay, Albany, W. Aust., to Robe, S. Aust.

Habitat. P. daveyae usually occurs in moderately deep water off coasts with moderate to strong wave action.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 196–197 (2003)]