Cleomella is a genus of about 22 species of annual wildflowers in the family Cleomaceae, order Brassicales. The genus is native to the arid and semi-arid regions of western North America, with a range extending from southern Mexico northward through the western and central United States into western and central Canada.
Plants in the genus are erect, branching annuals with compound leaves divided into three leaflets. They bear terminal inflorescences of yellow flowers with conspicuously long stamens, giving them a look closely resembling their relatives in the genus Cleome. Species are commonly called stinkweeds or cleomellas, a name that alludes to the pungent odor the foliage can produce when handled.
Cleomella was traditionally classified within the caper family Capparaceae, alongside Cleome and related genera. Modern molecular work prompted the recognition of a separate family, Cleomaceae, into which Cleomella — along with the rest of the spider-flower alliance — was transferred. The genus contains roughly 22 accepted species, including well-known taxa such as Cleomella obtusifolia (Mojave stinkweed), Cleomella lutea, Cleomella serrulata, and Cleomella parviflora (slender stinkweed).
Distribution
Cleomella species occur across the dry and desert regions of western North America, from southern Mexico northward through the western and central United States into western and central Canada. Individual species are often range-restricted: Cleomella obtusifolia is centered on the Mojave Desert, Cleomella refracta occurs in the Chihuahuan Desert region of northern Mexico and the southwestern United States, and Cleomella palmeriana occupies the Rocky Mountain foothills.
Taxonomy Notes
Cleomella was historically treated as part of the caper family Capparaceae. Phylogenetic studies revealed that the spider-flower clade (including Cleome, Cleomella, and allies) is more closely related to mustards (Brassicaceae) than to true capers, leading to its segregation into the family Cleomaceae within order Brassicales. The genus name Cleomella is a diminutive form of Cleome, reflecting its morphological similarity to that larger genus.
Ecology
Cleomella species grow in open, disturbed, and desert scrub habitats, typically on sandy or gravelly soils in arid to semi-arid regions. Their yellow flowers with long stamens attract a range of pollinators. The common name "stinkweed" reflects the pungent volatile compounds produced by the foliage, which may deter herbivory.
