Psilostrophe, commonly known as paperflowers, is a genus of flowering plants in the family Asteraceae (Compositae), placed within the tribe Helenieae (the sneezeweed tribe). The genus comprises biennials, perennials, subshrubs, and shrubs, ranging from 8 to 60 or more centimeters in height, with stems erect to spreading and branched from the base or throughout.
Leaves are arranged alternately and may be basal, cauline, or both. The blades are spatulate to oblanceolate or linear in shape, with margins that are usually entire, though occasionally toothed or lobed on larger rosette leaves. The leaf surfaces are densely to sparsely arachno-villous (cobwebby-hairy) or strigillose, and are often gland-dotted.
The flower heads are radiate and typically borne in compact corymbiform arrays or glomerulate clusters, though in P. cooperi heads are produced singly. Each involucre is cylindric to campanulate or obconic, 2–7 mm in diameter, with 5–12 phyllaries in one to two series that remain erect and persistent in fruit. Ray florets number 1–8 and are pistillate and fertile, with yellow to orange corollas that are notably marcescent — they persist and spread or reflex in fruit, giving the dried flowerheads a papery appearance that gives the genus its common name. Disc florets number 5 to 25 or more and are bisexual and fertile, also yellow to orange. The chromosome base number is x = 16.
Fruits (cypselae) are cylindric to clavate or obpyramidal, striate-ribbed, and usually glabrous; the pappus consists of 4–8 oblong to lanceolate entire scales.
Psilostrophe is native to southwestern North America, with species distributed across California, Nevada, Arizona, Utah, New Mexico, Colorado, Texas, Oklahoma, Kansas, and northern Mexico (including Chihuahua, Durango, Sonora, Baja California, and other Mexican states). The genus contains approximately 7–8 species commonly recognized in North America, with additional taxa described from Mexico.
Etymology
The common name "paperflowers" refers to the marcescent ray corollas, which persist and dry on the plant after flowering, giving the flowerheads a papery, tissue-like texture. The genus name Psilostrophe derives from Greek, though the precise classical etymology is not detailed in the primary botanical literature.
Distribution
Psilostrophe is native to southwestern North America, with species occurring across California, Nevada, Arizona, Utah, New Mexico, Colorado, Texas, Oklahoma, and Kansas in the United States, and extending into northern Mexico including Baja California, Baja California Sur, Sonora, Chihuahua, Durango, Coahuila, Nuevo León, Tamaulipas, San Luis Potosí, and Zacatecas.
Ecology
Plants grow in arid and semi-arid environments characteristic of the Sonoran, Chihuahuan, and Great Basin deserts and adjacent grasslands of southwestern North America. The genus spans elevational and habitat gradients across this region, with individual species occupying distinct geographic ranges within the broader southwestern distribution.
