Structure of a Phaeophyta
The phylum phaeophyta consists of over 1,500 different species of brown algae; all phaeophyta are multicellular. The smallest members of this phylum consist of only a few cells, and the largest members can grow up to 150 feet long. All phaeophyta range from olive green to various shades of brown. All brown phaeophyta are multicellular. Most phaeophyta do not have true stems, leaves, or roots; but they do have a holdfast. A holdfast is like an anchor that keeps it from moving. Most brown algae have one or more blades to cut through current or waves. Most brown algae also have stipes. A stipe is a stem like structure that runs throughout the body.
http://en.wikipedia.org/wiki/Brown_algae#Ecology
http://formosa.ntm.gov.tw/seaweeds/english/b/b3_02.asp
http://formosa.ntm.gov.tw/seaweeds/english/b/b3_02.asp