[1] Traditionally, it has been defined as containing single-celled flagellates with a cell wall.

There is generally a single chloroplast, which is often cup-shaped or sometimes stellate or discoid; pyrenoids may be present or absent.

[3] Sexual reproduction occurs in this family, and ranges from isogamy to anisogamy to oogamy.

Zygotes have thick walls, and they typically are inactive before germination.

[2] As accepted by WoRMS;[4] Former genera: The family is known to be non-monophyletic, with clades not aligning to traditionally defined morphological groupings.