Alaria marginata

Ribbon kelp

Authority: Postels & Ruprecht

Thallus of this common intertidal kelp is brown with a branched holdfast (haptera), a stipe, cylindrical near the base but flattened near the blade, that can reach 30 cm (12 in) or more in length; and a thin, lanceolate blade up to 3 m (10 ft) long with solid midrib. Twenty to forty elliptical sporophylls form in spring on the upper portion of the stipe and grow up to 25 cm (10 in) long, thickening with maturity.