Alaria marginata, the winged kelp, is a brown alga species in the genus Alaria. It can grow up to 13 feet. Fronds are long and narrow with raised midrib and wavy edges. Each frond has two rows of several smooth, oblong, 5 inch spore-bearing blades at the base in winter. The base is attached to rocks. In the kelp species Alaria marginata, phenolics act as chemical defence against herbivores.