Kelp (Laminaria sp. ) washed up on the shore of Holy Island, Northumberland, England. Kelp is brown algae & consists of a root-like structure, the holdfast, which anchors the organism; the stipe, which resembles the stem of a plant; and the blades, which are the part people generally recognise as seaweed. Kelps have long been harvested by humans for use as a dietary supplement, as a source of iodine, & as a potassium fertiliser.