Nyctaginaceae, the four o'clock family, is a family of around 33 genera and 290 species of flowering plants, widely distributed in tropical and subtropical regions, with a few representatives in temperate regions.

A phylogenetic study by Levin has justified the combination of Selinocarpus and Ammocodon into the genus Acleisanthes.

A more recent study by Douglas and Manos clarified the relationships among almost all of the genera in the family and demonstrated that a substantial diversification of herbaceous genera has occurred in arid North America.

Notable examples include sticky bands on the stems between the nodes, cleistogamous flowers (which self-pollinate without opening), or gypsophily, the ability to grow on soils with a high concentration of gypsum.

[11][12] The family contains one food crop, the mauka (Mirabilis extensa), a root vegetable of minor local importance in the Andes.