Echinosporangium semipennatum (Poir.) Kylin

Scientific Description

Habit and structure. Thallus medium to dark red-brown, 10–30 cm high, probably perennial, with robust branched axes 2–7 mm in diameter, bearing lesser branches with revolute apices developing a membranous, dorsal keel 1–2 mm broad and flat, ventral, determinate laterals 1–2 mm long, in 2 slightly divergent rows, alternating 2 segments apart; old axes heavily corticated, denuded but covered with irregularly branched, terete to compressed, appendages. Holdfast massive, first discoid but becoming branched, 3–30 mm across; epilithic. Structure. Apices revolute ventrally (towards the determinate laterals), apical cells dome-shaped, 15–20 µm in diameter, axial cells cutting off 6 pericentral cells, with dorsal and ventral cells and 2 lateral ones on each side; the dorsal cells divide longitudinally to form the keel and the 2 ventral lateral cells form the alternate determinate laterals separated by a single, unbranched cell. The keel is mostly 1 cell thick but may become 2 cells thick, and 17–22 cells broad with cells 35–75 µm in diameter and L/D 3–4. Determinate laterals are scalpelliform, terminally pointed, medially 10–14 cells broad, tapering to the acute tip, 1 cell thick apart from close to the indeterminate axis and the posterior margin which is 3 cells thick with alternate segments each bearing a trichoblast (absent near the tip). Trichoblasts become 2–3 mm long, branched, basal cells 20–35 µm in diameter and L/D 1–2. Old axes become heavily corticated with parenchymatous cells surrounding the 6 pericentral cells, and often covered with much branched, slender appendages 2–6 mm long, denuded near their base. Cells multinucleate; rhodoplasts discoid, becoming chained.

Reproduction. Gametophytes probably dioecious. Procarps on the second cell of the basal (and sometimes up to third) trichoblast on the determinate laterals. Carposporophytes with a small basal fusion cell and short gonimoblast with large, shortly clavate carposporangia 150–200 µm in diameter. Cystocarps subsessile, ovoid, 1–2 mm in diameter; pericarp ostiolate, heavily corticated, 5–8 cells thick. Spermatangia unknown. Tetrasporangia occur in series in the midrib adjacent to the keel, cut off from the ventral pericentral cells, covered by cortical cells which develop outward prolongations 1–3 cells and 80–130 µm long, 40–65 µm in diameter with rounded ends; tetrasporangia 250–500 µm in diameter.

Distribution. Eyre, W. Aust., to Port Elliot, S. Aust.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 329 (2003)]