General: Onyxflower (Achyronychia cooperi) is an annual forb that grows as a mat, often a starfish-shaped mat, flat on the ground. The leaves are oblong, fleshy, and opposite, but the leaf pairs are unequal; to about 3/4 inches long. The flowers are tiny, white, very numerous, and held in the leaf axils. The flowers can spread to cover the stems and most leaves, leading to another common name: frost mat, because it looks like morning frost on the plants. When the ground gets too hot, the stems bend upward into the air.

Onyxflower is a fairly common component of vegetation communities in heavy clay soils on the edges of playa basins as well as on dry, well-drained sandy and gravelly soils on desert flats and lower bajadas in the Lower Sonoran (Creosote-Bursage Flats) and Upper Sonoran (Mojave Desert Scrub) life zones to about 3,000 ft.

Around Las Vegas, look for Frost Mat mostly on desert flats, such as those around Lake Mead NRA and in the bottom of Death Valley.

Family: Pink (Caryophyllaceae)

Other names: Frost Mat, Onyx Flower, Starfish Plant