Undaria pinnatifida, known as wakame, is a brown kelp that grows from 1 to 3 meters. It has a small stipe and a large blade that is flattened and lanceolate, with wavy margins and a distinct central nerve. It is an annual species with two separate life stages.

Adapted from: 

Pereira, L. 2012. MACOI, Portuguese Seaweeds Website. World-wide Electronic Publication. IMAR, Department of Life Sciences, University of Coimbra, 

http://macoi.ci.uc.pt/spec_list_detail.php?spec_id=207.