Elisiella arbuscula (J.Agardh) Womersley

Scientific Description

Habit and structure. Thallus 2–6 cm high, somewhat complanately branched with several erect main axes bearing lateral branches more-or-less distichously from lower and central parts of the thallus, few from upper parts, each axial cell with 4 similar whorl-branchlets with the lateral branchlets often slightly more developed; lateral branches arising from basal cell of whorl-branchlets, especially from opposite lateral whorl-branchlets. Attachment by rhizoids from basal cells of axes, just penetrating the host cortex; epiphytic, usually on Cystophora spp. Structure. Apical cells 4–6 µm in diameter and L/D 1–1.5, enlarging rapidly to thick walled axial cells 80–130 µm in diameter and L/D 2–4(–7) in mid axes and 150–350 µm in diameter and L/D (1–)1.5–2 in lower axes. Whorl-branchlets coarse, more-or-less complanately branched and slightly upwardly curved, usually closely adjacent, (180–)200–350 µm long, branched from the basal cell with several successive subdi- (or tri- )chotomies and sometimes a terminal chain of 2–3 cells, often with a unicellular terminal hair; basal cells of whorl-branchlets 40–60(–90) µm in diameter and L/D 1–2, tapering to rounded terminal cells 8–12 µm in diameter and L/D 1–1.5(–2); gland cells prominent on terminal and subterminal cells of whorl-branchlets, hemispherical to ovoid, touching only the bearing cell or abutting the next upper cell, (12–)15–25 µm in diameter. Cells uninucleate; rhodoplasts discoid in small cells, becoming ribbon like in axial cells.

Reproduction. Gametophytes monoecious. Carpogonial branches borne near apices on short lateral indeterminate branches, on the basal cells of whorl-branchlets. Post-fertilization a terminal rounded gonimolobe 90–170 µm across with ovoid carposporangia 15–20 µm across develops, often with 1–2 lateral gonimolobes; basal procarp cells usually fuse. The carposporophytes terminate short lateral branches along the axes, without involucral branchlets apart from whorl-branchlets from below. Spermatangia are borne terminally on much branched clusters situated adaxially on lower cells of whorl-branchlets. Tetrasporangia when first formed appear sessile but when profuse they occur on branched clusters of ovoid cells, lying abaxially above the whorl-branchlet, subspherical, 25–50 µm in diameter, tetrahedrally divided.

Distribution. Cape Leeuwin, W. Aust., to Port Phillip Heads, Vic.

Habitat. E. arbuscula is a common species on rough-water coasts along most of southern Australia, usually epiphytic on Cystophora at or just below low tide level.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 194–197 (1998)]