Ironwood Olneya tesota A. Gray Fabaceae Species description Ironwood trees are broad-crowned evergreen or drought- deciduous, and native to the Sonoran Desert of the U.S. Southwest and northern Mexico. They occur at elevations below 2,500 ft. They may grow as single or multi-stemmed trees or large shrubs, usually along washes and on the lower foothills (bajadas) of desert mountains, and in xeroriparian corridors. The wood is finely grained and extremely dense (it does not float in water). Younger branches have sharp thorns. The grey bark is smooth on younger branches and peeling on the older branches and trunks. Ironwood leaves are pinnately compound, oblong, grey-blue-green, and finely haired, and may occur singly and alternate or in clusters. Each leaflet may be slightly asymmetric, with the tips entire, blunted or notched. The foliage is dense, and tardily drought-deciduous. The white to pale-purple heavily scented flowers appear in June. They produce 1-8 seeded, light to red-brown, rounded, hairy leguminous pods. Ironwood trees are very slow growing, and they may reach 15-45 feet in height with trunks 15-25 inches diameter. Certain individuals have lived for 1,500 years. Natural and cultural history Ironwood trees are native to the desertscrub and thornscrub of the Sonoran Desert. They occur along dry, ephemeral washes, and less freQuently on rocky slopes, plains and open valleys. Native Americans cooked and leached the seeds to be eaten. Planting considerations and propagation techniques Ironwood trees are very slow growing and long-lived; their selection should be a careful, intentional addition to desert food forests. Ironwood is a keystone species, and may be used as a nurse plant to protect other, more sensitive plants. In its natural environment, ironwood offers shade to many smaller desert plants and fixes nitrogen in the soil to improve fertility. Ironwood prefers full sun, and the species grow on a range of soils, from sandy to rocky, with a pH of 7-8.5. Ironwood trees are frost sensitive; the stems will suffer damage below 20ºF, though they may grow in colder areas in planted in sheltered areas. Ironwood flowers are insect pollinated. The species is propagated by seed. They do not need stratification, but germinate better if they are soaked 24 hours before planting. Water needs Ironwood is naturally a xeroriparian species, reQuiring more water than some desert plants, but still highly drought tolerant. Care The trees are heavily thorned and should be pruned to shape. Harvesting and processing The edible flowers may be gathered in May and June. Harvest ironwood pods when they are still gold-green, and the seeds are tender. Ironwood seeds can be roasted and eaten, sprouted, or ground into flour. References and resources Felger, R.S., M.B. Johnson, and M.F. Wilson. 2001. The Trees of Sonora, Mexico. Oxford University Press, Oxford, UK. Krugman, S. L. 1974. Olneya tesota A. Gray. In Seeds of Woody Plants in the United States, edited by C. S. Schopmeyer. Agricultural Handbook #450. Forest Service, U.S. Department of Agriculture, Washington D.C. University of Arizona Pima County Cooperative Extension. 2006. Olneya tesota: Desert ironwood. https://ag.arizona.edu/pima/gardening/aridplants/Olneya_tesota.html. Accessed June 17, 2015. Spellenberg, Richard, Christopher J. Earle, and Gil Nelson. Trees of Western North America. Princeton University Press, 2014. 2 .