Xanthisma, commonly known as sleepy-daisy, is a genus of flowering plants in the family Asteraceae (the daisy family), order Asterales. The genus comprises roughly ten species of annual and perennial herbs native to western and central North America, with the greatest diversity in the arid and semi-arid regions of the southwestern United States and northern Mexico.
Plants in this genus typically bear yellow, daisy-like flower heads with ray florets surrounding a central disc — a form characteristic of the broader tribe Astereae. The common name "sleepy-daisy" is thought to refer to the habit of ray florets closing at night or in overcast conditions, a response seen in several Asteraceae genera.
Xanthisma was first formally described in 1836 from specimens gathered in what was then "The Mexican Province of Texas." The genus was later substantially revised, with a number of species formerly placed in Machaeranthera and related genera transferred to Xanthisma following molecular phylogenetic work by Morgan and Hartman. The broadly distributed Xanthisma spinulosum (spiny sleepy-daisy) is one of the best-known members, ranging from Alberta and Saskatchewan south through the Great Plains and Rockies to Texas and northern Mexico. Xanthisma texanum is endemic to the Chihuahuan Desert region of Texas, New Mexico, and Arizona.
Etymology
The name Xanthisma derives from the Greek xanthos ("yellow") and -ismos ("condition" or "state"), a reference to the bright yellow ray florets that characterize most species in the genus. The genus was first described in 1836 from material collected in "The Mexican Province of Texas."
Distribution
Xanthisma is native to western and central North America. Species occur across a broad latitudinal range from Alberta and Saskatchewan in the north through the Great Plains, Rocky Mountains, and Basin-and-Range provinces to the states of Texas, New Mexico, Arizona, and California, with several species extending into northern Mexico (Chihuahua, Coahuila, Durango, Nuevo León, and Baja California).
Taxonomy Notes
The genus has been subject to significant taxonomic revision. Several species now placed in Xanthisma were previously treated under Machaeranthera or related genera; the transfers were formalized by D.R. Morgan and R.L. Hartman based on molecular phylogenetic evidence. GBIF currently recognizes 3 accepted species in its backbone, while the Wikipedia species list enumerates 10, reflecting ongoing differences between taxonomic treatments.
