Description: Thallus of this dark brown kelp has a branched holdfast (haptera), a stipe, cylindrical at the base, flattening above, up to 50 cm (20 in) long, and an elliptical blade to 150 cm (60 in) long and 28 cm (11 in) wide with a distinctive thick, broad midrib 5 cm (1.75 in) wide. The blade is puckered along the sides of the midrib. The stipe and holdfast are perennial while the blade is annual and dies back in the fall. Habitat: This species occurs on rock in the extreme low intertidal and upper subtidal of semi-exposed habitats or high current areas.