Ectocarpus siliculosus is a filamentous brown alga (Heterokontophyta).Its genome was the first brown macroalgal genome to be sequenced, with the expectation that E. siliculosus will serve as a genetic and genomic model for brown macroalgae. The alga is unbranched and filamentous; it forms soft beards on larger plants or other firm substrata and grows up to 2 feet long.

Further reading:

The Ectocarpus genome and the independent evolution of multicellularity in brown algae. Nature. 465(7298), 617-21 (2010). [pubmed]