Ectocarpus is a genus of filamentous brown alga (Heterokontophyta) that is a model organism for the genomics of multicellularity. Among possible model organisms in the brown algae, Ectocarpus was selected for the relatively small size of its mature thallus and the speed with which it completes its life cycle. The type species for the genus is Ectocarpus siliculosus (Dillwyn) Lyngbye.