Olneya tesota

Original Watercolor of Desert Ironwood, Olneya tesota, © by Michael Plagens

Watercolor from live specimen found near New River, Maricopa Co., Arizona, 30 May 1993.

Habit of Desert Ironwood, Olneya tesota, © by Michael Plagens

Observed at Papago Park in Phoenix, Arizona, USA. October 2011. The small shrubs growing nearby include Creosote Bush (Larrea tridentata) and Triangle-leaf Bursage (Ambrosia deltoidea).

TREE: An important and sometimes large tree occasionally taller than 12 meters. The bark of young branches is light to dark gray; older bark is dark gray and deeply fissured. Upper lateral branches often arch downwards reaching the ground level.

RANGE: Wash banks throughout the Sonoran Desert below 500 m elevation. This tree is a good indicator of frost severity and was used as a guide to an area's suitability for citrus cultivation. Southwest Arizona, southeast California and south into Mexico.

ARMED: Sharp and slightly curved spines occur in pairs at each node.

LEAVES: Leaves are pinnately compound and evergreen. There are usually an even number of leaflets, i.e. slightly offset pairs and no terminal leaflet. Six to 20 leaflets. Well into the severe droughts evergreen Desert Ironwood presents an unseemly verdant. Stems and leaves are all covered with short, matted pubescence. At the base of each compound leaf are a pair if acute stipules - these may either fall off or else grow longer and harden into paired thorns.

FLOWERS: In May a profusion of lilac-colored flowers makes this one of the most beautiful desert plants. Typical pea-type flower.

FRUIT: Bean pods are covered with a short, slightly sticky pubescence and turn burgundy-brown as they ripen. Edible seeds have a flavor resembling peanuts.

Fabaceae -- Bean Family

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wood of dead Desert Ironwood, Olneya tesota, © by Michael Plagens

This tree lived in the Mohawk Mts. of Yuma Co., Arizona, and might have been hundreds of years old. How long ago it died and how long it will take for the wood decay is unknown. A tug on a branch showed that almost no decay has taken place so far! View a bigger image on Flickr.

More Information:

Sonoran Desert Field Guide
Sonoran Desert Places
Sonoran Desert Naturalist Home Page


Copyright Michael J. Plagens, page created 6 Nov. 2007,
updated 2 March 2016.