Polyopes constrictus (Turner) J.Agardh

Scientific Description

Habit and structure. Thallus dark red-brown to olive-brown, 4–16 cm high, cartilaginous, with dense, spreading to fastigiate tufts of numerous fronds. Fronds individually more or less complanately branched, irregularly subdichotomous at intervals of 3–10 mm (longer near the base), linear, compressed and 0.5–2.0(–2.5) mm broad, apices rounded, branches with occasional constrictions above. Holdfast discoid, 2–5(–15) mm across; epilithic. Structure of a firm cortex of anticlinal rows of dichotomous filaments 5–8(–12) cells long above, becoming longer in lower parts, outer cells 1.5–3 µm in diameter in surface view, elongate-ovoid in section, becoming larger to the inner cortex, and a dense medulla of longitudinal and anastomosing filaments 3–6 µm in diameter; some inner cortical cells slightly stellate, refractive ganglionic cells absent. Rhodoplasts discoid, becoming ribbon shaped and branched, few per cell.

Reproduction. Sexual thalli dioecious. Carpogonial branch ampullae situated in the inner cortex, relatively simple with a few short secondary filaments, carpogonial branches 2–celled. Auxiliary cell ampullae situated in the inner cortex but protruding into the outer medulla, larger and much branched, with moderately long secondary and tertiary filaments (up to 5 orders) of ovoid cells, often becoming profusely branched, and a basal auxiliary cell, later forming a moderately prominent involucre (with lower cells becoming elongate) around the carposporophyte which lies in the outer medulla and inner cortex; carposporangia subspherical to ovoid, 8–12 µm in diameter; ostioles small and narrow, formed by separation of cortical filaments. Spermatangia forming a surface layer on upper branches, elongate, 0.5–1.5 µm in diameter, with subspherical spermatia. Tetrasporangia in oval to elongate nemathecia on upper branches, borne among paraphyses 40–60 µm and 4–8 cells long, lower cells 2–4 µm in diameter and L/D 4–6, upper cells isodiametric and similar to outer cortical cells. Tetrasporangia elongate, 24–30 µm long and 6–10 µm in diameter, cruciately divided.

Distribution. South Africa. Sleaford Bay, S. Aust., to Twofold Bay, N.S.W., and around Tas.

Habitat. P. constrictus is moderately common from shallow but often shaded situations to 20 m deep.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 175–176 (1994)]