Olneya tesota is a perennial flowering tree of the family Fabaceae, legumes (peas, beans, etc.), which is commonly known as ironwood, desert ironwood, or palo fierro in Spanish. It is the only species in the monotypic genus Olneya. This tree is part of the western Sonoran Desert in Mexico and United States.

The desert ironwood grows as a bush or tree, reaching heights of about 10 metres (33 feet) and average trunk diameters of about 60 centimetres (24 inches). Exceptionally, in larger protected washes it can reach greater height and a more massive trunk.

In younger trees, the bark is gray, shiny, and smooth; in older trees the bark is broken open. The tree is evergreen, but can lose its leaves if temperatures fall below 2 °C (36 °F). In continual drought conditions the leaves will be lost.

The leaves are bluish-green and pinnately compound. They are arranged on a petiole, 15 cm (6 in) long, with 6–9 leaflets (or variously up to 15, with 7 opposite and one terminal), each measuring 0.7 to 2.5 cm (1⁄4 to 1 in). At the base of each pinnate leaf petiole grow two thorns, each about 1 cm (3⁄8 in) long.

Bloom time occurs in late April/May to June. Flowers are of 5 unequal petals, in colors of medium purple, magenta-red, or white to pale pink. Seedpods are 5–8 cm (2–3 in) long and light reddish brown when seedpods have ripened.

Two other species, Parkinsonia florida (blue palo verde) and Acacia constricta (catclaw acacia), have similar light red/brownish seedpods. Catclaw acacia's seedpods are shorter and J-shaped.

The genus name of Olneya is in honour of Stephen Thayer Olney (1812–1878), who was an American manufacturer and botanist with expertise in the genus Carex.

The genus was circumscribed by Asa Gray in Pl. Nov. Thurb. page 328 in 1854.