Any of about 30 genera of large seaweeds that make up the order Laminariales (brown algae ), found in colder seas.
Laminaria , abundant along the Pacific coasts and the British Isles, is a source of commercial iodine . Its stipe (stemlike structure) is 3–10 ft (1–3 m) long. The largest known kelp, Macrocystis , grows up to 215 ft (65 m) long. Its body, which has a large rootlike holdfast, a hollow stipe, and branching blades with hollow gas bladders, resembles that of higher plants. It is rich in minerals and algin, a complex carbohydrate used as an emulsifier to prevent crystal formation in ice cream. Species of kelp are widely eaten in East Asia.