Coeloclonium verticillatum (Harv.) J.Agardh

Scientific Description

Habit and structure. Thallus medium to dark brown-red, 5–15 cm high, densely branched with axes and branches bearing whorls (usually not synchronous) or clusters of lesser branches as well as single branches; axes 1–2 mm in diameter with 0.5–1.5 cm between whorls, lesser branchlets elongate-clavate to linear, basally constricted but not segmented, 5–10 mm long and 1–2(–3) mm in diameter, apices rounded to slightly depressed. Holdfast discoid or divided, clasping host; usually epiphytic on Amphibolis, Laurencia and other algae. Structure. Apical filament short, on broad, rounded or slightly depressed apices, apical cell hemispherical, 12–18 µm in diameter. Pericentral cells 5, transversely elongate, becoming 40–90 µm in diameter and L/D 4–6, with arms extending down along the axial cell and uniting with the lower pericentral cell, also producing further rhizoids. Pericentral cells branched tri- or quadrichotomously for 2–3 orders, with an outer cortex 1–2 cells thick, outer cells (20–)30–40 µm in diameter and L/D 2–3(–4), in longitudinal rows. Older branches becoming filled with rhizoids between the pericentral and their derivative cells. Trichoblasts on apical filaments. Cells uninucleate; rhodoplasts discoid, chained in larger cells.

Reproduction. Procarps not observed. Carposporophytes with a basal filamentous cluster and branched gonimoblast with clavate terminal carposporangia 40–80 µm in diameter, borne on slender strands. Cystocarps ovoid, sessile, 1.5–2 mm in diameter; pericarp with a broad ostiole, ecorticate, 2–3 cells thick. Spermatangial organs not observed. Tetrasporangia borne on the pericentral cells or their derivatives, one to few per whorl, 80–150(–200) µm in diameter.

Distribution.Rottnest I., W. Aust., to Port Phillip Heads, Vic., and around Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 415–417 (2003)]