Parkinsonia microphylla Torr.

by Kirsten Larsen, Native Plants of Arizona 2004
Common names: Yellow paloverde, littleleaf palo verde, foothill palo verde (1,2,4), hillside paloverde, littleleaf horsebean (4).
Family: Fabaceae (1,9).
Synonymy: Cercidium microphyllum (Torr.) Rose & I.M. Johnston (1), Cercidiopsis microphylla Britton & Rose (6).
Etymology: Parkinsonia honors the English botanist John Parkinson. The former genus name Cercidium used in many of the published references below signifies the resemblance of the legume to a Greek weaver’s comb or shuttle, a kerkidion (7,8). The specific epithet, microphylla (or former microphyllum), refers to small leaves (8).

Identification
Growth form: Tree up to 8 m. tall, trunk up to 0.3 m. in diameter, crown spreading 3.7-5.5. m., branching about 20 cm from the ground into 4-6 major stems (2,4).
Roots:
Stem: Thin, smooth, glaucous, yellow-green, photosynthetic bark. Twigs terminally spinose up to 5.1 cm. long, no nodal spines (2,3,4).
Leaves: Alternate, sessile, drought deciduous, yellow-green, bipinnately (even-2-pinnate) compound, pubescent, 2.5 cm. long (2), 1 pair of pinnae, each with 4-8 pairs of minute, <3 mm. long, 1-1.8 mm wide, elliptical leaflets (3,4,5,6,7).
Inflorescence/flowers: Inflorescence a raceme, axillary, <7 flowers (7). Flowers pale yellow, slightly bilateral. Sepals +/- free and all alike. Petals 5, upper petal (banner) creamy white (4,6,7). circular, about 5 mm. in diameter, the claw 3 mm. long, the rest of the petals ovate attenuate, 5-6 mm. long, 3-5 mm. wide (6). Stamens 10, exerted, free, filaments hairy at base (3,7).
Fruit: Puberulous legumes 4-8 cm. long, 1 cm. wide, constricted between seeds (2,3,6), pod turgid, ending in a flat triangular or sword shaped beak (5), 1-5(4) seeds (2,6). Seeds 7-8 mm. long, brown oblong-ovoid (3).
Similar species: Parkinsonia florida has larger leaflets, bright yellow flowers, blue-green bark, nodal spines, and flowers earlier (4,6). Has been known to hybridize (2,7).

Ecology
Life history: Small tree or shrub (2,9), perennial (1,9).
Native/introduced: Native to the Southwestern United States (9).
Photosynthetic pathway:
Phenology: Flowers April to May (3).
Distribution: Through central and southwestern Arizona, a few populations occur in southeastern California near the Colorado River (2,5) in the Whipple Mountains, extending southward through Sonora and Baja California, Mexico. An indicator species of the Sonoran Desert floristic
region and a dominant species in the upland portion of the Sonoran Desert. Found on bajadas and rocky slopes throughout the Sonoran Desert and grades into adjacent semidesert grasslands and interior chaparral (2,6). Northern Mohave County to Cochise, Pima, and Yuma Counties 4,000 feet or lower on dry rocky hillsides and mesas of Arizona (5). 500-3,500 ft. elevation (6).

Uses
The Yuma Indians roasted and ground the seeds for mush, or parched the seeds till almost burnt as a famine food. The Papago Indians basket winnowed, parched, sun dried, cooked, stored, ground, the seeds as a dry and staple food source. The Pima Indians ate the green pods raw or boiled (10,2). Cultivated as an ornamental (2,7). Ungulates can browse the twigs and leaves and small mammals and rodents consume the seeds. Also used by breeding birds for nesting, foraging, and as roosts. White throated woodrats use for shelter or nests. Collared peccary consume fruits from July to September (2). Arizona state tree (4).

References
1. Retrieved [November, 12, 2004], from the Integrated Taxonomic Information System on-line database, http://www.itis.usda.gov.
2. Pavek, Diane S. 1994. Cercidium microphyllum. 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/ [2004, November 12].
3. McDougal, W.B. 1973. Seed Plants of Northern Arizona. The Museum of Northern Arizona. Flagstaff, Arizona.
4. Epple, A. O. 1995. A Field Guide to the Plants of Arizona. Falcon Publishing. Helena, Montana.
5. Kearney, T. H., R. H. Peebles, and collaborators. 1960. Arizona Flora 2nd Edition. University of California Press, Berkeley and Los Angeles, California.
6. Benson, L. and R. A. Darrow. 1981. Trees and Shrubs of the Southwestern Deserts (3rd ed). University of Arizona Press, Tucson.
7. Hickman, J. C. (ed).1993. The Jepson Manual; Higher Plants of California. University of California Press, Berkley and Los Angeles, California.
8. Vines, R. A. 1960. Trees, Shrubs, and Woody Vines of the Southwest. University of Texas Press, Austin, Texas.
9. USDA, NRCS. 2004. The PLANTS Database, Version 3.5 (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
10. Moerman, D. 2003. Native American Ethnobotany Database (http://herb.umd.umich.edu/). University of Michigan, Dearborn, MI 48198 USA.