Undaria

Undaria pinnatifida, commonly known as wakame, is a large brown alga in the family Alariaceae. It is a kelp with a holdfast that anchors to rocky or artificial substrates, a stalk, and many flexible blade-like fronds. Thalli can reach several meters in length and are olive-brown; they contain gas-filled bladders that help buoyancy. Like other kelps, its life cycle includes a sporophyte phase and microscopic haploid stages.

Native to temperate coastal waters of the western Pacific, including Japan, Korea, and China, Undaria has been introduced to many regions and is considered invasive in numerous non-native habitats. It commonly occurs in shallow subtidal zones and can colonize rocky shores, pilings, and aquaculture structures. It grows rapidly under favorable temperatures and nutrient conditions.

In invaded areas, Undaria pinnatifida can outcompete native macroalgae and alter local communities by shading and space monopolization. It spreads through natural dispersal, rafting, and human activities such as hull fouling and aquaculture. Management emphasizes early detection, manual removal, and containment, though eradication is difficult in open coastal systems.

Despite its invasive status in many places, Undaria is also valued as a food seaweed in East Asia, where wakame is harvested commercially and consumed in soups, salads, and garnishes. Cultivation has spread to other regions for food and research, including bioremediation and biomaterials.