Areschougia ligulata J.Agardh

Scientific Description

Habit and structure. Thallus medium to dark red, cartilaginous, 10–35 cm high, much branched irregularly and more-or-less complanately from the margins at intervals usually of 1–4 cm, branches strongly compressed, (2–)2.5–4 mm broad in main branches, 2–3 mm in laterals, lesser branchlets 1–2 mm broad, linear with constricted bases and rounded to pointed apices, margin smooth or with small proliferations, with a faint to conspicuous midrib. Holdfast discoid-conical, becoming robust and hapteroid, (2–)5–20 mm across, with a single stipe; epilithic. Structure uniaxial, with each axial cell cutting off a single periaxial cell on three radii but becoming subopposite on successive cells, forming a lax medulla of periaxial filaments and a pseudoparenchymatous cortex 5–6 cells thick, inner cells ovoid and 20–40 µm in diameter, outer cells 4–6 µm in diameter and L/D 1–2; rhizoidal filaments soon filling the medulla, with the axial filament conspicuous throughout; cortical thickening occurs near the base, especially over the midrib (axial filament). Rhodoplasts discoid, becoming ribbon shaped, several per cell.

Reproduction.Sexual reproduction non-procarpic. Carpogonial branches 3(–4)-celled, borne on outer medullary cells, directed inwards or sideways with reflexed trichogynes, occasionally with sterile cells on the lower cells. Connecting filaments 4–7, non-septate and unbranched, uniting with the auxiliary cell (an outer medullary or inner cortical cell), with adjacent cells becoming darkly staining and cutting off nutritive filaments. Gonimoblast initial first inwards, later radial from the fusion cell (with a stalk) and producing short chains of ovoid carposporangia 15–20 µm in diameter. Cystocarps in small clusters of 2–5, protruding on the flat surface of branchlets, with lax filamentous enveloping tissue, ostiolate. Spermatangia unknown. Tetrasporangia scattered in the cortex of young branches, developed from mid cortical cells and pit-connected basally, ovoid, 40–50 µm long and 20–25 µm in diameter, zonately divided.

Distribution.Geraldton, W. Aust., to D' Estrees Bay, Kangaroo I., S. Aust.

Habitat. A. ligulata appears to be a deep-water alga on rough-water coasts.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 360 (1994)]