Palo Verde Parkinsonia florida (Benth. ex A.Gray) S. Wats.; Parkinsonia microphylla Torr. Fabaceae

Species description Palo verde is a small, monoecious native tree with thin, green photosynthetic bark and a spreading crown. Palo verde trees have spiny, irregular branches and very small, pinnately compound leaves. The leaves have a bluish-green coloring in blue palo verde (Parkinsonia florida) and tend toward yellow- green in the smaller, shrubbier foothills palo verde (P. microphylla). The leaves are drought deciduous, emerging after rainfall and falling during dry periods. In spring, numerous yellow flowers emerge in clusters on the branchlets. Blue palo verde trees can have a spectacular golden crown of flowers. The leguminous pods of both species are 2-3 inches long with small seeds.

Natural and cultural history Palo verde trees are native to the southwestern U.S. and Mexico and grow in a wide variety of habitats, including slopes, ridges, bajadas, plains, and arroyos. Foothills palo verde can usually be found on slopes and plains, while blue palo verde prefers desert washes with ironwood and mesquite. They occur from sea level to 4,000 feet in elevation. Native Americans used the seeds of both species as a food resource. The seeds may be eaten fresh or dried, though dried seeds must be soaked and cooked. Southwest tribes cooked ground seeds into porridge.

Planting considerations and propagation techniques Palo verde tree growth rates vary by species; foothills paloverde is a slow growing, smaller shrub-like tree, while blue palo verde are moderate to fast growing tall, spreading trees. Blue palo verde trees may grow to 25-30 feet in height and width. They are long-lived and drought tolerant. As desert trees, palo verde are hardy to about 10ºF. In natural environments, palo verde serve as nurse trees for other species; they drop nitrogen-rich leaf, seedpod, branch, and blossom litter to the ground. Birds nest in them and fertilize the ground beneath. This creates a protected, rich germination zone beneath the trees for saguaro cacti and other desert plants. Desert animals also seek refuge and food from palo verde trees.

Water needs Palo verde trees may need supplemental irrigation to establish, but they are a drought tolerant species. Blue palo verde, a xeroriparian species, may need more water than foothills palo verde.

Care Palo verde trees are insect pollinated, and the bright yellow flowers attract a myriad of bees. They should be planted in full sun on well-drained soils. Palo verde trees may be easily propagated by seed; however they do hybridize and care should be taken in selection. The trees are generally disease resistant, however, cultivated blue palo verde trees may be damaged by mite infestations. True mistletoe can also affect all palo verde species. Manual removal is only practical solution, though it will continue to grow within tree branches. Since mistletoe is a part of the desert ecology, it is an aesthetic decision whether to remove it or not on lightly infested trees. Mistletoe berries are a primary food source of desert birds and only in few situations the mistletoe becomes large enough to warrant removal. Palo verde root borer may also affect trees. Blue palo verde trees generally require more pruning than foothills palo verde because they tend to spread and have more secondary branches. Pruning of the latter can include raising the crown base height to give the tree a more urban-friendly form.

Harvesting and processing The flowers and seeds of both species are edible. Green and dry pods can be harvested, preferably before the summer monsoon rains. To harvest the green seeds, select green pods when the seed inside has developed but is still small and tender. When green, the seeds can be eaten fresh or cooked like peas. The green seeds should be sweet. Dry seeds are best eaten sprouted, or sprouted and then parched/roasted. To sprout the seeds, soak them overnight and rinse daily until seed coat splits open and the sprout emerges. Remove sprouts by squeezing the split seed coat. Rinse the seeds with clean water and then use the sprouts raw or lightly cooked. To parch/roast the sprouted seeds, sprout them until just the tiny root emerges (1-2 days). Dry the seeds in the sun, solar oven, or oven set to 150 F. Once dry, put the seeds in a skillet over medium heat to cook until they pop. They may be seasoned with salt or other spices.

References and resources Arizona State University. n.d. Parkinsonia florida. http://www.public.asu.edu/~camartin/plants/Plant%20html%20files/parkinsoniaflorida.html. Desert Harvesters: Appreciating the native foods of the Sonoran Desert, palo verde. http://www.desertharvesters.org/native-plant-food-guides-the-desert-can-feed-you/palo-verde/ Pavek, Diane S. 1994. Parkinsonia florida. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/. Pavek, D. S. 1994. Parkinsonia microphylla. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/. Spellenberg, Richard, Christopher J. Earle, and Gil Nelson. Trees of Western North America. Princeton University Press, 2014.

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