Areschougia congesta (Turner) J.Agardh

Scientific Description

Habit and structure. Thallus dark brown-red, 10–40 cm high, much branched irregularly with terete (to slightly compressed) linear to tapering branches, basally constricted with rounded to pointed apices, above 300–800 µmin diameter, mid branches 0.4–1 mm in diameter, becoming 1–2(–4) mm broad (slightly compressed) in lower axes. Holdfast discoid, 2–10 mm across, with a single axis (rarely several); epilithic. Structure uniaxial, with each axial cell producing a single periaxial cell, on three radii on successive cells, forming a lax medulla of periaxial filaments (soon becoming filled with rhizoids, densely below) and a pseudoparenchymatous cortex 4–8 cells thick, inner cells ovoid and 20–40 µm in diameter, outer cells 4–6 µm in diameter, L/D 1–1.5; axial filament conspicuous throughout the thallus, and the older parts thickened by a cortical meristem. Rhodoplasts discoid, becoming ribbon shaped, several per cell.

Reproduction. Sexual thalli dioecious; non-procarpic. Carpogonial branches 3(–4)-celled, borne on inner cortical cells, directed inwards or sideways with reflexed trichogynes, the hypogynous or basal cell usually with 1–2 sterile cells. Connecting filaments 3–5, non-septate, occasionally branched, uniting with the auxiliary cell which is an outer medullary or inner cortical cell, with adjacent cells becoming darkly staining after diploidization and cutting off nutritive filaments. Gonimoblast initial first inwards, later radial from the fusion cell with a prominent stalk, producing short chains of ovoid carposporangia (20–)30–60 µm in diameter. Cystocarps swelling the upper branches, with lax filamentous enveloping tissue and the adjacent cortex increasing in thickness and becoming ostiolate. Spermatangia in nemathecia on young branches, in clusters between clavate paraphyses 24–35 µm long, ends 4–6 µm in diameter, with outer cortical cells cutting off 2–3 mother cells each producing 2–4 ovoid to pointed spermatangia 2–4 µm in diameter. Tetrasporangia scattered within the cortex, developed from inner cortical cells and laterally pit-connected to adjacent cells, ovoid, 80–110 µm long and 50–70 µm in diameter, zonately divided.

Distribution.Hamelin Bay, W. Aust., to Walkerville, Vic., and around Tas. Lord Howe I.(?).

Habitat. A. congesta is a common alga in southern Australia, especially on rough-water coasts, extending into calmer situations.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 356–360 (1994)]