Achyronychia cooperi
Onyx flower, frost-mat, Frost-Mat
Photo by Chez Brungraber
Family: Caryophyllaceae · Type: Herb · Native
Achyronychia cooperi (Onyx flower) is a native California herb in the Caryophyllaceae family, recognized by Southwestern US endemic genus with specialized desert adaptations not found in other Caryophyllaceae.
Onyx flower is a California native annual found in southern California desert bioregions in sandy slopes, flats, and washes at elevations of 50 to 700 meters. Flowering from January to May, this delicate plant produces tiny white flowers in clusters of 20 to 60 blooms. Growing with prostrate to ascending stems 3 to 17 centimeters tall, it spreads in low, delicate patches across sandy terrain. Its leaves are oblanceolate, somewhat fleshy, and 3 to 20 millimeters long, with distinctive white-fringed scarious stipules. The fruit is a small utricle with 8 to 10 minute teeth, containing a single tan seed with a distinctive red dot near its narrow end.
Identification and appearance
Key characters: Southwestern US endemic genus with specialized desert adaptations not found in other Caryophyllaceae
Habitat and range
Habitat: Sandy slopes, flats, washes
Elevation: 50-700 m
California counties: San Bernardino, Riverside, Imperial, Inyo, San Diego, Shasta, Kern
Outside California: Arizona, Mexico
Bloom period
Achyronychia cooperi blooms Jan-May.
How to tell it apart
vs Euphorbia: Achyronychia has pink family flowers with many thread bristles; Euphorbia has milky sap.; vs Paronychia: Achyronychia has broad rounded sepals; Paronychia has narrow bristle-tipped sepals.; vs Cardionema: Achyronychia is desert annual; Cardionema is coastal woolly perennial.; vs Herniaria: Achyronychia has broad rounded sepals; Herniaria has narrow blunt sepals.; vs Scopulophila: Achyronychia is annual with thread-like staminodes; Scopulophila is woolly-based perennial with petal-like staminodes.
Frequently asked questions
Is Achyronychia cooperi native to California?
Yes. Achyronychia cooperi is native to California (recorded as native).
When does Achyronychia cooperi bloom?
Achyronychia cooperi blooms Jan-May.
Where in California does Achyronychia cooperi grow?
Achyronychia cooperi occurs in San Bernardino, Riverside, Imperial, Inyo, San Diego, Shasta, Kern, at elevations of 50-700 m.
What plant family does Achyronychia cooperi belong to?
Achyronychia cooperi is in the Caryophyllaceae family, genus Achyronychia.
What habitat does Achyronychia cooperi grow in?
Achyronychia cooperi grows in Sandy slopes, flats, washes.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.