Achyronychia is a monotypic genus in the pink family (Caryophyllaceae), containing a single species: Achyronychia cooperi, commonly called onyxflower or frost-mat. The genus was described in 1868 by Asa Gray in the Proceedings of the American Academy of Arts and Sciences.
Onyxflower is a diminutive, prostrate annual that grows flat against the ground in a small mat, radiating several short stems only a few centimeters long in all directions. Its thick, pale green leaves are paddle-shaped and under two centimeters long. The flowers are tiny and clustered densely in the leaf axils. They lack petals entirely; instead, each flower bears five thin, shiny white sepals that resemble tiny fingernails — the feature that inspired the genus name, which derives from the Greek for "chaff fingernail."
The plant is a specialist of sandy desert habitats in the Mojave and Sonoran Deserts, ranging from northern Mexico through southern California, southern Nevada, southwestern Utah, and western Arizona.
Etymology
The genus name Achyronychia derives from Greek, meaning "chaff fingernail," in reference to the plant's five thin, shiny white sepals, which lack petals and are said to resemble tiny fingernails.
Distribution
Achyronychia cooperi is native to the Mojave and Sonoran Deserts of northern Mexico and the southwestern United States, including the desert regions of California (San Diego, Imperial, Riverside, Los Angeles, San Bernardino, and Inyo Counties), Arizona (Yuma, Mohave, Pima, Pinal, and Maricopa Counties), southern Nevada (Clark County), and southwestern Utah (Washington County). It grows exclusively in sandy habitats.
