Agarum clathratum

Thallus blade-like, coarse, coriaceous, to 1 m long and to 50 cm broad, oval or roundish in outline, with undulate or smooth margins, often with a ragged top, cordate base, olive-brown to almost black in color, single or in groups in association with laminarian algae. Midrib percurrent, prominent or flattened, up to 2 cm wide. The blade with numerous, irregularly located perforations on the whole surface; from 0.5 to 1 cm in diam. (commonly the largest perforations are situated along the midrib). Stalk short (2–15 cm), compressed or long, slender, to 30 cm. Sporangial sori develop in the middle portion on both surfaces of the blade. Attached to the substratum by welldeveloped, long, branched rhizoids. Growing in the low intertidal to subtidal (to 20 m depth), on rocky, stony and sandy-muddy bottom with stones and shells, on semi-protected coasts.

Arctic (Canada), Pacific and Atlantic Oceans coasts of North America. Common in countries of the Asia-Pacific Region: China, Korea, Japan and Russia (the Bering Sea, the Sea of Okhotsk, the Sea of Japan).