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 complex in the Southwestern United States, which includes flora such as palo verde, saguaro, ocotillo, brittlebush, creosote bush.

The desert ironwood grows as a bush or tree and reaches heights of about 10 meters (33 ft), and average trunk diameters of about 60 cm (24 in); in exceptional sites in larger protected washes it can reach a 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 an evergreen plant but can lose its leaves if temperatures fall below 2 °C (36 °F). In continual drought conditions, leaves will be lost.

Leaves are bluish-green and pinnately compound. Leaves are arranged on a petiole, 6 in (15 cm) long, with 6-9 leaflets-(or variously up to 15, 7, 7-opposite, and one terminal), each being 0.7 to 2.5 cm (0.28 to 0.98 in). At the base of each pinnate leaf petiole grow two thorns, about 1 cm (0.39 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 also white to pale pink. Seedpods are 5–8 cm (2–4 in) long, and light reddish brown when seedpods are 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 noticeably J-shaped and of shorter length.

Observations Map

The desert ironwood, Olneya, is native to the southwestern United States and extreme northwestern Mexico in the Baja California Peninsula and the Sonoran Desert and is partially an indicator species of that desert. Within Mexico, its range includes the states of Baja California Sur and Baja California, on the Gulf of California side east of the Cordillera ranges, and Sonora state west of the Sierra Madre Occidental Cordillera, in the south approaching the northern border of northern Sinaloa state. In the southwestern US, its range includes the Colorado Desert of southeast Southern California, a part of the Sonoran Desert, and western and southern Arizona. Olneya does not range into the higher-elevation, colder, southeast of Arizona's Sonoran Desert region, nor into the sky islands of the Madrean Sky Islands region. Ironwood Forest National Monument in south-central Arizona is named for Olneya tesota.

Olneya tesota is an indicator species of the Sonoran Desert region. The Sonoran Desert has one other species with the identical north-south, and east-west range. The seasonally migrating lesser long-nosed bat follows the bloom season of various species from south to north and extends into the same regions of the Sonoran Desert as Olneya; (their ranging maps are virtually identical). The bat ranges from southern Baja California del Sur and north into the southwestern United States.

In the north, both species define the Colorado Desert subregion of the Sonoran Desert surrounding the northern end of the Gulf of California; further south in the Baja Peninsula the sub-division is defined as the Vizcaino Desert.

The winter and permanent range of the bat extend into the northern countries of Central America.


The pleasant-tasting sap is consumed by bees and hummingbirds. The silky-flycatcher or phainopepla pose a problem, for when they consume mistletoe berries and excrete them in the cracks of Olneya tesota, the mistletoe will parasitize its host.

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