Amansia pinnatifida Harv.

Scientific Description

Habit and structure. Thallus medium to dark red-brown, 10–40 cm high, much branched alternately marginally and complanately with flat, linear, branches (1.5–)2–3 mm broad, slightly constricted basally and with ventrally circinnate apices, margins entire, midrib clear on dorsal side, the cells in surface view in transverse tiers with the ends of the 2 layers overlapping alternately, ecorticate. The ventral surface of branches invariably bears an almost complete cover of the bryozoan Bathypora nitens. Lower axes denuded of most laterals, 2–4 mm broad, the midrib secondarily thickened. Holdfast discoid-conical, 2–20 mm across; epilithic. Structure. Apex circinnate, apical cell hemispherical, 12–18 µm in diameter, axial cells cutting off 5 pericentral cells, 2 lateral on each side and 1 ventral, with the dorsal-lateral cells each cutting off a pseudopericentral cell and the lateral cells dividing rapidly to produce the 2 cell-thick wings with mature cells 35–50 µm in diameter and L/D 5–6, ends dovetailing. The midrib develops secondary thickening first ventrally, spreading laterally and later also dorsally. Trichoblasts not observed. Cells multinucleate; rhodoplasts discoid, chained in larger cells.

Reproduction. Gametophytes dioecious. Reproductive organs borne on short, spinous, marginal shoots. Procarps on reduced trichoblasts on these shoots, soon polysiphonous and pericarpic. Carposporophytes with a basal fusion cell and much branched gonimoblast with clavate terminal carposporangia 30–50 µm in diameter. Cystocarps on margins, with a short, thick, stalk, globose to ovoid, 500–1200 µm in diameter; pericarp ostiolate, 4–6 cells thick. Spermatangial organs clustered on short, branched, marginal laterals, with a basal sterile cell, ovoid, 90–180 µm in diameter. Tetrasporangial stichidia (1–5) on short marginal spinous branchlets, curved to circinnate, compressed, corticated, 0.5–1.5 mm long and 150–300 µm broad, with 2 rows of paired tetrasporangia 70–110 µm in diameter.

Distribution.King George Sound, W. Aust., to Robe, S. Aust.

Habitat. A. pinnatifida is a deep-water alga of distinctive habit.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 392–394 (2003)]