The Phaeophyceans are quite diverse and produce a great amount of biomass in marine systems. They range from microscopic filaments to giant kelps which have significant tissue and cellular specialization. The brown algae contain chlorophylls a and c, beta-carotene, and fucoxanthin in the plastids.
Plastids typically possess a girdle lamella and a periplastidal endoplasmic reticulum.
The photosynthetic reserve material in the Phaeophyceans is laminaran, a beta-1,3 glucan. The Fucales differ from the other groups of the Phaeophyceans primarily in its reproduction. The Fucales do not exhibit alternation of generations. Instead, gametes are formed from the 2N thallus by mieosis followed by mitosis. The Sargassaceae exhibit radial branching that is more or less continuous from the base to the apex.