Antrocentrum nigrescens (Harv.) Kraft & Min-Thein

Scientific Description

Habit and structure. Thallus medium to dark red-brown, 5–20 cm high, much branched irregularly with percurrent axes or main branches and terete, slender, laterals, 0.7–1.5 mm in diameter, tapering to a point gradually or abruptly, often proliferous when damaged, occasionally with recurved branch ends. Holdfast densely fibrous, branched, 0.5–2 cm across, bearing one to several fronds; epilithic or epiphytic. Structure. Apices uniaxial with a prominent apical cell, cells of axial filament each with two adjacent periaxial cells, rotated on successive cells, forming a lax filamentous medulla (central filament soon inconspicuous), becoming densely filamentous below, and a cortex of large, isodiametric to slightly radially elongate inner cells 20–30 µm across and a small-celled outer cortex 1–2 cells thick, outer cells ovoid to pointed, 4–6 µm in diameter, L/D 1–2, forming distinct to indistinct rosettes in surface view. Rhodoplasts discoid, becoming ribbon shaped, many per cell.

Reproduction. Sexual thalli monoecious; probably procarpic. Carpogonial branches borne singly on inner cortical cells, 3-celled, directed inwards with reflexed trichogynes. Supporting cell apparently acting as auxiliary cell, with adjacent vegetative filaments developing centripetally to form a broad enveloping tissue. Gonimoblast initials cut off thallus inwardly, then growing over the inside of the enveloping tissue as the auxiliary cell disintegrates, forming centripetal tufts of filaments with terminal ovoid carposporangia 20–30 µm in diameter. Cystocarps embedded, 0.7–1 mm in diameter, with prominent enveloping tissue and thickened cortex, ostiolate. Spermatangial clusters scattered, with outer cortical cells producing several initials each forming 2–3 ovoid spermatangia. Tetrasporangia scattered, developed from mid cortical cells, laterally pit-connected, ovoid, 30–50 µm long and 20–35 µm in diameter, zonately divided.

Distribution.Yanchep, W. Aust., to Collaroy, N.S.W., and the N coast of Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 373–374 (1994)]