Сostaria costata

Thallus consisting of blade, stipe and branched rhizoids. The blade linear-lanceolate, broadly linear to oval, coriaceous, smooth, 1.0-2.0 m long, (5)-10-30 cm broad, olive to brown, with five percurrent longitudinal prominent ribs coming together at the base. The middle rib and ribs near to margins prominent on one side and two other ribs (in between the midrib and marginal ribs) prominent on the other side of the blade. Spaces between the ribs smooth or with bullae. Narrow blades with cuneate bases and broad blades with oval and broadly cordate bases. Margins flat, slightly undulate or entire. Stipe cylindrical at base, compressed above and with marked furrows. Sporangial sori in patches scattered over surface of the thallus. Growing on rocky, stony and muddy-sandy bottom with stones, boulders and blocks, in low intertidal to upper subtidal (to 10 m depth), at shores exposed to moderate and strong wave action.

Arctic to temperate waters of Pacific Ocean. Japan, Korea and Russia.