a class of brown algae that includes the highly specialized order Fucales. The thallus, which is parenchymatous, with differentiated tissues, consists of a base, a central shoot, and lateral branches. The algae develop in the diploid phase. Reproduction is oogamous. Longitudinal growth is effected by one or more apical cells, and latitudinal growth by the division of the outer layer of cells. Chloroplasts in the vegetative cells have no pyrenoids. The reproductive organs are formed in conceptacles.
The class includes 37 genera, embracing approximately 450 species. The algae are widely distributed in the world ocean. Many species are used to produce alginic acids for the food-processing and textile industries.