The walls are made of cellulose and alginic acid, a long-chained heteropolysaccharide. The vast majority of the Phaeophyta are marine in distribution. About 190,000 tonnes of the brown kelp Macrocystis are harvested each year off the coasts of California and Mexico for extraction of alginic acid. This is used commercially for toothpastes, soaps, ice cream, tinned meats, fabric printing, and a host of other applications. It forms a stable viscous gel in water, and its primary function in the above applications is as a binder, stabilizer, emulsifier, or moulding agent.
Most brown algae have an alternation of haploid and diploid generations.
The haploid thalli form isogamous, anisogamous or oogamous gametes and the diploid thalli form zoospores by meiosis. There are about 3,000 species of brown algae, and most of them are marine.