Callithamnion byssoides Harv.

Scientific Description

Habit and structure. Thallus erect and spreading, medium red-brown, tufted, 5–15 mm high, main axes weakly defined apically, clearer below, bearing radially shorter lateral branchlets which are branched 2–4 times, ecorticate. Attachment by spreading rhizoids from basal cells of erect axes, sometimes producing further erect axes; epiphytic on gelatinous Rhodophyta (e.g. Gloiosaccion, Platoma foliosa, Tsengia comosa). Structure. Apical cells 3–6 µm in diameter and L/D 2–5, ends of apical cells rounded, increasing to 8–12 µm in diameter and L/D 2–4 at 2–3 cells below their apices, increasing gradually to 30–40 µm and L/D 3–5 in mid cells and in lower axes 80–120 µm in diameter, cells L/D (1–)1.5–2(–6), with thick gelatinous walls; lateral branchlets branched 3–4 times, lower cells 20–30(–35) µm in diameter and L/D 2–3(–4). Cells uninucleate; rhodoplasts discoid to elongate.

Reproduction. Gametophytes dioecious. Procarps borne on mid cells of the upper axes or main branches, with two periaxial cells one of which (the supporting cell) bears the 4-celled carpogonial branch; post-fertilization each periaxial cell cuts off an auxiliary cell which produces a branched carposporophyte with tapering lobes of ovoid carposporangia (10–)15–30 µm in diameter. Spermatangia borne on short branched filaments 3–4 cells long, ovoid, 1.5–3 µm in diameter. Tetrasporangia sessile on cells of the lateral branchlets, subspherical, 25–45 µm in diameter, tetrahedrally to decussately divided.

Distribution. From Esperance, W. Aust., to Port MacDonnell, S. Aust.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 248–250 (1998)]