a large group of Phaeophyceae. (According to one system they are a class.) The sporophytes of Heterogenerataephyceae are macroscopic. They are 1 cm to several meters tall and sometimes have a complex structure. The gametophytes are microscopic.
Heterogenerataephyceae are often divided into two subclasses. Polystichineaephycidae are forms in which the cells are divided by longitudinal septa, and a true parenchymatous tissue forms. Haplostichineaephycidae are forms in which the thallus consists internally of threads, which form pseudoparenchymatous tissue, and in which the cells are not divided longitudinally. Heterogenerataephyceae are widely found in the seas. Algae of the genus Laminaria have the greatest practical significance.