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Scientific: Parkinsonia microphylla (formerly Cercidium microphyllum)
Common: foothills or little leaf palo verde, yellow palo verde
Family: Fabaceae (Leguminosae)
Origin: Widely distributed within upland foothill subdivisions of the Sonoran Desert in eastern California, Arizona, and into Sonora and Baja California.

Pronounciation: Par-kin-SONE-ee-a my-crow-FIL-la

Hardiness zones:
Sunset 10-14, 18-20
USDA 9-10 (arid regions only)

Landscape Use: Xeric and/or native desert gardens as a small multi-branched tree or large background shrub.

Form & Character: Upright, open, rounded and spreading, very stiff and pokey, intricate terminal branching, arid.

Growth Habit: Partially deciduous, woody perennial, spiny shrub to small tree, moderately slow growth to 15 to 25 feet in height with equal spread greatly dependent on site water availability.

Foliage/Texture: Tiny pinnately compound leaves, 4 to 8 pairs leaflets, short terminal spur branches that growth to a stiff and spine like tip, leaves, stems and branches are all medium to yellowish green, photosynthetic; fine texture.

Flowers & Fruits: Pale yellow pea-shaped flowers followed by short, brownish pods in mid summer that abscise all at once.

Seasonal Color: Pale yellow flowers in late May just after Parkinsonia florida and Parkinsonia praecox.

Temperature: Tolerant

Light: Full sun

Soil: Tolerant, but grows best in a coarse, well-drained to gravelly soil.

Watering: Little to none once established, though it will grow faster with supplemental water.

Pruning: Prune only if necessary by elevating canopy base, train early to avoid large wounds. Wear full PPE (leather gloves, long sleeve shirts and pants, protective eye wear, etc.) when working with this well-armed plant, otherwise expect to get injured.

Propagation: Seed, acid scarification of seeds in 95% sulfuric acid for 30 min to 1 hr followed by a 15 minute rinse in cool to tepid water. Sow immediately thereafter.

Disease and Pests: Larvae of palo verde root borers (Derobrachus geminatus) feed on these trees. They grow up to 4 inches in length. Adult beetles are up to three and one half inches long with long antennae. No chemical treatment is effective, instead treat by promoting tree vigor. Parkinsonia microphylla and Parkinsonia praecox are subject to a condition called "trunk blister" in Phoenix urban landscapes, the casual agent as yet has not been identified. Mistletoe on Parkinsonia microphylla and Parkinsonia florida can be problematic and should be removed immediately.

Additional comments: Foothills palo verde (along with blue palo verde) is the Arizona state tree. Foothills palo verde is stiffer, smaller and less refined compared to its 'big blue brother', Parkinsonia florida. In the nursery trade, it's not widely available because of slower growth, smaller size and a more deciduous habit.

A final observation: The locally native foothills palo verde is quite at home naturalizing anywhere in the Phoenix area where there's a bit of topography.