Undaria pinnatifida is a large brown alga belonging to the Laminariales. It has three easily distinguishable parts comprising its visible thallus: blade, stipe and holdfast. Plants can reach an overall length of one to three metres. It is an annual species with two different stages of life. Undaria pinnatifida can be found in the upper part of the infralittoral (subtidal) zone, from low tide level down to depths of 10 to 18 meters. 

Cited from:

http://macoi.ci.uc.pt/spec_list_detail.phpspec_id=207&searchSpecies=undaria+pinnafitida+%28harvey%29+suringar