sw United States, nw Mexico, introduced in other regions.
The status of Simmondsiaceae has long been controversial; it has previously been included in the Euphorbiales, either submerged in Buxaceae or as a separate family near Buxaceae (A. Cronquist 1981), or in the Hamamelidae as its own order (A. L. Takhtajan 1997). Recent molecular phylogenetic evidence supports recognition as a monogeneric family with a near-basal position in the Caryophyllales (P. Cuénoud et al. 2002; K. W. Hilu et al. 2003; Angiosperm Phylogeny Group 2003; S. F. Brockington et al. 2009).