The genus sensu stricto includes about 170 species of herbaceous annual or perennial plants and shrubs.

[4] The genus has a subcosmopolitan distribution throughout the tropical and warm temperate regions of the world.

This, combined with it being very close to the Brassicaceae with the model plant species Arabidopsis thaliana, makes it an ideal genus in which to study the evolution of C4 photosynthesis.

Morphological differences that demonstrate the transition from C3 to C4 include C3 species having leaves with more veins and larger bundle sheath cells.

C. houtteana is a commonly cultivated ornamental plant with purple, pink, or white flowers.