Arizona State Tree
Palo Verde (common name)
genus Parkinsonia (scientific name)
The name "palo verde" means "green branch" or "green tree" in Spanish. The trees have thin, green bark on their trunks and branches. During dry times, which may be most of the year where palo verde grows, the tree will shed its delicate leaves to conserve moisture. Although leaves are absent most of the year, photosynthesis, the manufacture of food, is performed by the chlorophyll in the trunk and branches. Arizona's state tree is a true desert dweller, and it frequently grows in the company of the saguaro cactus, Arizona's state flower. The palo verde often serves as a "nurse plant" for saguaro cacti—the cactus seedlings require a shaded, moist environment in their first few years of growth. Saguaro eventually outlive or contribute to the death of palo verde trees.
Palo verde is an attractive, small tree increasingly used as a street tree in the desert southwest. Three similar palo verde species are native in the Sonoran Desert of Arizona. Yellow palo verde has a yellowish hue to its branches and foliage. Blue palo verde has blue-green branches and foliage. The tree is probably best known for its bright yellow flowers that cover the tree in spring.
Arizona's state tree was designated in 1954. The legislation does not select a particular species of palo verde, but only specifies the genus. The blue palo verde and yellow palo verde both grow in the desert and desert foothill regions of the Southwest United States. Jerusalem thorn, another species of palo verde, can be found in 13 states across the south, from South Carolina to California, as well as Puerto Rico and the Virgin Islands.
Palo verde is a small, native, rounded tree, with branches low on the trunk. Branches of blue palo verde often droop to the ground. Twigs are typically spiny. Compound leaves with small leaflets vary among the three species. Flowers are yellow and showy, and fruit is a bean pod with hard seeds.
Blue palo verde grows to nearly 33 feet tall with a trunk diameter of one to two feet and a crown spread of over 160 square feet (15 sq m). Yellow palo verde may grow to 26 feet (8 m) tall, and the trunk may be 1 foot (0.3 m) in diameter. Yellow palo verde branches about 8 inches (20 cm) from the ground into four to six major stems, and its crown spreads 12 to 18 feet (3.7-5.5 m). The bark of both species is thin and photosynthetic.
Height: 26-33 ft (8-10 m)
Diameter: 1-1.5 ft (0.3-0.5 m)
Bark: thin, photosynthetic
Seed: yellow palo verde: bean pod, 2-3 in (4-8 cm) long
1-5 seeds with constrictions between the seeds
blue palo verde: flat legumes, 1.5-4 in (4-10 cm) long, each legume holds 1-8 flat seeds
Leaves: compound with small leaflets
Yellow palo verde lives longer than 72 years, often over 100 years, and may reach 400 years. Blue palo verde grows faster and dies sooner, rarely reaching the century mark.
Both yellow and blue palo verde are native to central and southern Arizona, southeastern California, and northwestern Mexico. Blue palo verde is found along washes and valleys and sometimes on lower slopes of deserts and desert grasslands. Yellow palo verde grows with Saguaro cactus on desert plains and rocky slopes of foothills and mountains. Yellow palo verde shares its habitat with white burrobrush, white ratany, organpipe cactus, and MacDougal ocotillo. Blue palo verde grows near honey mesquite, smoketree, ironwood, desert willow, catclaw acacia, and desert lavender.
IMPORTANCE TO LIVESTOCK AND WILDLIFE
Twigs and pods of palo verde serve as food for wildlife and emergency food for livestock. The seeds are consumed by rodents and birds. The flowers are a source of honey.
Blue palo verde fruits, twigs, and leaves are used as livestock forage throughout the year. Mule deer, bighorn sheep, jackrabbits, burros, and other small mammals browse its twigs and leaves. Numerous birds forage, perch and/or nest in the abundant branches. Small mammals consume blue palo verde seeds during summer and fall.
In southern Arizona, birds nest in blue palo verde taller than 6.5 feet (2 m). With a large canopy, blue palo verde offers many sites for bird perching, nesting, and foraging. In south central Arizona, 19 species of breeding birds have been found in wooded areas where blue palo verde grows.
OTHER USES AND VALUES
Native Americans ate seeds and seedpods and also ground seeds for gruel. Palo Verde seeds were a known food source for the Cahuilla, Pima, and Papago Indians. The Pima carved blue palo verde into large serving spoons.
During their short flowering seasons, both species are covered with thousands of five-petaled yellow blossoms. Many pollinators, including beetles, flies, and bees, are attracted to palo verde. Animals disperse seeds, and birds probably move seeds upstream.
Both species also reproduce asexually. In a greenhouse study, young blue palo verde sprouted after plants were clipped to less than one-half of their total height. Yellow palo verde has fair to poor ability to produce sprouts after top removal.
Both species grow in arid to semiarid climates with mild winters and hot summers, where precipitation occurs only in summer and fall. Blue palo verde grows on terraces, high flood plains, arroyos or dry washes, and intermittent streambeds. It occupies hills, mountain slopes, and middle to lower bajadas. Blue palo verde grows in soils with low levels of nutrients. Yellow palo verde is found on lower mountain slopes and alluvial outwash plains. In the most arid parts of its range, yellow palo verde occasionally occurs in small washes or arroyos.
Blue palo verde is found at elevations from sea level to 4,000 feet (0-1,220 m), while yellow palo verde occurs from 1,000 to 4,000 feet (305-1219 m). Both species grow on gradual to steep slopes facing south or north.
Click to enlarge an image
U.S. Forest Service
U.S. National Arboretum
U.S. Department of Agriculture
Author: World Trade Press