Dieteria is a small genus of flowering plants in the family Asteraceae (order Asterales), native to western North America. The genus was described by Thomas Nuttall and comprises a handful of species — sometimes called "tansyasters" — that grow across the arid and semi-arid landscapes of the western United States, western Canada, and adjacent northern Mexico.
Plants in Dieteria are herbaceous annuals or perennials with alternate leaves that are entire to shallowly toothed along the margin. This leaf character is the key feature separating Dieteria from its closest relative, Machaeranthera, whose leaves are once or twice pinnately divided. Flower heads are daisy-like and typical of the tribe Astereae: ray florets surround a central disc, producing the characteristic composite inflorescence that defines the family.
The genus has a predominantly western North American distribution, with species found across California, Nevada, Arizona, New Mexico, Colorado, Utah, Wyoming, Oregon, and into the Canadian west, as well as the Mexican states of Chihuahua and Durango. Dieteria canescens is the most widespread species, occupying most of this range. Dieteria bigelovii and Dieteria asteroides have more restricted distributions within the southwestern United States and adjacent Mexico.
Taxonomy Notes
Dieteria (Nutt.) is placed in the family Asteraceae (tribe Astereae) and is most closely allied to Machaeranthera. The two genera differ in leaf morphology: Dieteria has entire to toothed leaves, while Machaeranthera leaves are once or twice pinnately lobed. Some species formerly placed in Machaeranthera have been transferred to Dieteria following molecular phylogenetic work by D.R. Morgan and R.L. Hartman.
Distribution
Dieteria is native to western North America. The most widespread species, Dieteria canescens, ranges across most of the western United States and western Canada and south into Chihuahua, Mexico. Other species — D. bigelovii, D. asteroides, and D. shastensis — are more localized within the southwestern United States, ranging from California and Nevada east through Arizona, New Mexico, and Colorado, and north into Utah, Wyoming, and Oregon.
