Hymenocladia divaricata Harv.

Scientific Description

Habit and structure. Thallus yellow-red to red-brown, 5–18 cm high, much branched with compressed branch axes 2–3(–5) mm broad centrally, bearing marginally and irregularly compressed laterals 2–10 cm long, and 1–2(–3) mm broad, often with lesser laterals, and all branches densely covered with slender, simple or irregularly branched, subterete ramuli (0.5–)1–2(–3) mm long and (100–)150–250 µm in diameter; ramuli mostly distichously arranged but flexed out of the plane, with some irregularly placed or from the branch surfaces, apices relatively acute. Holdfast discoid, 1–3 mm across; epiphytic on Amphibolis, or epilithic (?). Structure probably multiaxial but apices narrow, developing a cortex 1–2 cells thick, outer cells ovoid and 4–5 µm in diameter, grading over 2–4 cells to the medulla 4–6 cells across, the large inner cells ovoid and 70–140 µm in diameter with walls thin (to 10 µm thick), with intermixed filaments of smaller elongate cells 5–12 µm in diameter; secondary pit-connections frequent. Rhodoplasts elongate, ribbon like in inner cells.

Reproduction. Gametangial thalli monoecious. Carpogonial and auxiliary cell branches unknown. Carposporophytes with a basal, branched, fusion complex with the upper cells all forming carposporangia, with secondary lobes developing later; carposporangia ovoid, 45–90 µm in diameter. Basal nutritive tissue prominent, with cells of the erect filaments largely disintegrating but some lower thick-walled cells remaining. Cystocarps scattered on lesser branches on the surface or edges, hemispherical and broad based, 1–2 mm in basal diameter, pericarp 130–220 µm and 8–14 cells thick, inner cells ovoid, with a prominent ostiole. Spermatangia in small sori, cut off from elongate initials, ovoid, 1.5–2 µm in diameter. Tetrasporangia scattered, transformed from intercalary outer medullary cells, subspherical, 70–100 µm in diameter, tetrahedrally divided.

Distribution.King George Sound, W. Aust., to Cape Jaffa, S. Aust.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 109–111 (1996)]