Halimeda opuntia

Thallus forming loose clumps or extensive colonies, 40-50(-100) cm in diameter, to 25 cm high; dark green, whitish yellow-green. Branching irregular, in all planes or at right angle with each other. Segments heavily calcified, flat to contorted, ribbed, transversely oval, ear-shaped, trilobate, 6-17 mm wide, 5-10 mm long, 0.3-0.5(-1.2) mm thick. Joints flexible. The outermost utricles polygonal in surface view, angular or slightly rounded. In longitudinal section of segment cortex composed of 3-4(-5) layers of utricles. Surface utricles (12)-25-30(-60) mm diam., 30-60 mm long. Subsurface utricles (11)-30-50 mm diam., (30)-40-55 mm long, each bearing 3-4(-5) surface utricles. Attachment by fibrous holdfast to 3 cm diam. and by secondary rhizoids developing from any segment touch to the substratum. On dead corals, covered with sand, in shallow lagoons, intertidal to subtidal.

Subtropical and tropical waters of Atlantic, Indian and Pacific Oceans.