Phacelocarpus alatus Harv.

Scientific Description

Habit and structure. Thallus medium to dark red-brown, (10–)15–40 cm high, with a single, slightly compressed stipe 5–25 mm long and 2–3 mm broad, giving rise to several long, straight, complanately branched, compressed, main branches bearing laterals irregularly for 3–4 orders. All branches bearing distichous, compressed, alternate, pointed ramuli 500–900(–1000) µm long, shorter than the rachis width of 750–1250(–1500) µm, the latter with a central raised midrib and "winged" margins. Holdfast discoid, 2–4 mm across; epilithic. Structure uniaxial, developing a prominent axial filament becoming surrounded by dense rhizoids (forming the midrib), and with pairs of lateral periaxial cells on alternate segments which develop to form the alternate ramuli. Cortex pseudoparenchymatous, inner cells ovoid and 10–20 µm in diameter, outer cells 1.5–3 µm in diameter and L/D 1–2; refractive cell inclusions conspicuous in the outer cortex; rhodoplasts discoid, few per cell.

Reproduction.All reproductive bodies borne on short to distinct stalks from the rachis, between the ramuli. Sexual thalli dioecious. Procarps in small branchlets, with two carpogonial branches and a prominent auxiliary cell. Cystocarps stalked, 400–600 µm across, bilabiate, with a thick pericarp enclosing the carposporophyte with a basal fusion cell producing a laterally elongate tuft of gonimoblast filaments with terminal single (–2) elongate-ovoid carposporangia 6–8 µm in diameter. Spermatangia in channels in globular, stalked, nemathecia. Tetrasporangia within globular, short-stalked, nemathecia 250–400 µm in diameter, separated by tufts of sterile filaments, elongate, 40–50 µm long and 6–12 µm in diameter, zonately (often irregularly) divided.

Distribution.Rottnest I., W. Aust., and Port Elliot, S. Aust., to Walkerville, Vic.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 393–395 (1994)]