Involucrana crassa (Hook.f. & Harv.) Gordon-Mills

Scientific Description

Habit and structure. Thallus dark red-brown, 5–20 cm high, branched alternately and distichously for 3–4 orders, with some long branches with hamate tips, erect axes arising from prostrate basal branches or from a matted holdfast 2–10 mm across; epiphytic on larger algae or possibly epilithic. Structure. Subapical cells forming opposite, distichous pairs of whorl-branchlets, with occasionally a third and rarely a fourth opposite the third, axial cells 600–800 µm in diameter and L/D 2–5 below. Mature whorl-branchlets 2.5–4 mm long, spreading and overlapping, subpolychotomous at their base and subtri- to dichotomous above, ultimate branches of 1–3 cells, ends of terminal cells rounded, median cells 200–300 µm in diameter and L/D 2.5–6; further laterals are produced from basal cells of whorl-branchlets in the lower thallus, obscuring the distichous arrangement of whorl-branchlets. Indeterminate branches arising in the position of whorl-branchlets on axial cells; on some branches the axial cells near apices bear reduced, or no, whorl-branchlets and the end becomes curved. Cortication of lower axes occurs by rhizoids from the lower ends of cells. Cells multinucleate; rhodoplasts discoid to elongate.

Reproduction. Gametophytes dioecious. Female axis of 3 cells, arising distally and adaxially from the subterminal cell of a young whorl-branchlet, the subapical cell bearing two pericentral cells, one (the supporting cell) bearing a terminal sterile cell and a lateral carpogonial branch; fusion cell lobed, with anastomosing processes bearing terminal clavate carposporangia 35–50 µm in diameter; carposporophyte 450–700 µm across; 3 inner involucral branchlets surround the carposporophyte, with an outer involucre from the lower whorl-branchlets. Spermatangial heads ovoid, 80–100 µm in diameter, situated on reduced branch systems borne on lower to upper cells of whorl-branchlets. Polysporangia with 27–32 spores, 100–220 µm in diameter, occur, borne on terminally or laterally on lower cells of whorl-branchlets, surrounded by curved involucral filaments arising from the basal cell.

Distribution.Elliston, S. Aust., to Gabo I., Vic., and N and E Tas.

Habitat. Involucrana crassa is a deep water alga, known mainly from drift specimens, on rough-water coasts; rarely it occurs in shallow, shaded situations.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 76 (1998)]