Desert tree identification in the American Southwest

Green bark: the palo verdes

Green bark tells you at once that you are looking at a palo verde. The park service explains that the green comes from chlorophyll in the bark of the branches and the main trunk.

• Foothill (yellow) palo verde (Parkinsonia microphylla): yellow-green bark, tiny drought-deciduous leaves, pale yellow flowers one to two weeks after the blue palo verde, and no thorns. The most common tree in the Tucson Mountain District of Saguaro National Park, mainly on hillsides and the upper bajada.
• Blue palo verde (Parkinsonia florida): blue-green bark, leaves that are fewer and larger than the foothill's, showy bright yellow flowers in spring, and small thorns. It grows in sandy washes at the bottom of the bajada and out into the valley.

The trees with yellow flowers guide covers other yellow-flowered trees.

Dark bark and pods: the mesquites

Mesquites have dark trunks, feathery leaves split into many small leaflets, and long bean pods.

• Velvet mesquite (Prosopis velutina): larger leaves than the other legume trees of Saguaro National Park, soft and fuzzy gray-green; trunk and big branches dark gray to almost black, small branches greenish; pale yellow flowers in catkins; flat tan pods, sometimes streaked with red, 8 to 15 cm (3 to 6 inches) long according to the USDA NRCS velvet mesquite plant guide. It dominates the lower elevations of the park.
• Honey mesquite (Prosopis glandulosa): hairless leaves, usually with two primary leaf sets of 8 to 20 narrow leaflets each; thorns 1 to 2 inches long, usually single on young branches; fragrant greenish-yellow flowers in narrow clusters up to 3 inches, March to August; straight, reddish-brown pods 7 to 20 cm (3 to 8 inches) long, constricted between the seeds, according to the USDA NRCS honey mesquite plant guide. It grows about 20 feet tall in bottomlands, washes and sandy flats, from 0 to about 5,000 feet (University of Arizona Cooperative Extension).

Honey locust, another legume with thorns and long pods, is covered on the locust page. For other trees with pods, see the long seed pods guide.

Thorns and purple flowers: desert ironwood and other legumes

• Desert ironwood (Olneya tesota): gray-green leaves smaller than mesquite's; pale lavender, pea-shaped flowers in late spring; short, slightly curved thorns on the branches. It grows at low elevations in the Sonoran Desert.
• Whitethorn acacia (Vachellia constricta): a shrubby tree with tiny leaflets, reddish new branches that fade to gray, yellow ball-shaped flowers in late spring and straight white thorns, common in washes and small drainages.

Thorns on all of these can cut skin and clothing; the trees with thorns guide covers thorny trees across the US. Never eat a pod, seed, berry or flower on the strength of a web page or an app; check with a local expert.

Washes and springs: desert willow and fan palm

• Desert willow (Chilopsis linearis): narrow, light green leaves up to 10 inches long and 3/8 inch wide; fragrant, orchid-like flowers in pink, lavender or white with purple and yellow streaks in the throat, April to August; long, narrow, slightly twisted seed capsules. Up to 29 feet tall in dry washes and on river terraces from 0 to 5,000 feet. Despite the name, University of Arizona Cooperative Extension places it in the catalpa family, not with willows.
• California fan palm (Washingtonia filifera): native to the low, hot deserts of southern California, up to 75 feet tall, with dead fronds hanging down the trunk like a brown skirt until fire, wind or flood removes them. The park service counts only 118 desert fan palm oases in North America, seven of them in Joshua Tree National Park, usually where a fault forces groundwater to the surface. The palm page separates the California and Mexican fan palms.

The Mojave: Joshua tree

The Joshua tree (Yucca brevifolia) marks the Mojave Desert. It has tough, sharp, dagger-like leaves at the ends of thick, branching arms, and clusters of white-green flowers at the branch tips from mid-February into April in years with well-timed rain and a winter freeze. Most reach about 40 feet, rare giants 50. In Joshua Tree National Park it grows between 2,800 and 5,800 feet. DNA work places it in the agave family; it is a monocot, not a woody tree. The close relative Mojave yucca has longer, broader leaves with fibrous threads along the edges (National Park Service).

Using a photo in the desert

Desert leaves are tiny and can be missing in drought, so photograph more than one feature: the bark, a thorn, a pod or a flower. Tree Identifier names a plant from one photo, and its follow-up chat can answer "blue palo verde or foothill palo verde?". It needs a data connection, which remote trails may lack, so take the photos and identify them later from your library. It shows no confidence score, so check the answer against the table above. Mesquite, palo verde and Joshua tree are not among the 138 species of the app's Collection; finds outside it are kept under Wild Discoveries, and the Tree Map remembers where each one grew. For yard and street trees nationwide, see the most common trees in the US.