May 2008 Arizona’s state tree, the Palo Verde, is named for the distinctive green trunks and branches, but could easily be named Nube Amarillo for the bright yellow clouds they become when in bloom. There are three wild species, the Littleleaf Palo Verde, Blue Palo Verde and Mexican Palo Verde. A hybrid of all three, dubbed the “Museum Variety,” is commonly used in landscaping and combines the best features of each species into a drought hearty thornless tree with large showy yellow flowers.
April and May is show time for Palo Verdes in the Sonoran desert. On the dry rocky slopes of Deem Hills, the Littleleaf, a.k.a. Foothills Palo Verde (Cercidium microphyllum), is super abundant. Their natural form is more like a large shrub, with branches growing in a roundish tangle that drapes to the ground, creating shade for sun sensitive young saguaros and thick growths of annual wildflowers. These slow-growing trees live to several hundred years old, providing food and shelter to many species of wildlife, including javelina, rock squirrels, rabbits and hares, many species of birds, beetles and over twenty native species of bee. Thick growths of mistletoe also attract birds that feed on the berries. Palo Verde seeds, pods and flowers are edible for humans as well, and provided a main source of food for early Native Americans in the desert. The delicate pale yellow flowers of Littleleaf Palo Verde develop into woody pods that look like strings of beads. Along washes and in floodplains, the Blue Palo Verde (Cercidium floridum) is more common, and is easily distinguished from the Littleleaf by the bright yellow flowers and graceful, upward sweeping branches. Their pods are broad, flat and papery compared to their cousins in the foothills. Because they grow where there is more moisture, the wood is softer and they also live only to about one hundred years old rather than several centuries.
The scrubby Mexican Palo Verde (Parkinsonia aculeata) is the thorniest species, and has an orange or orange-speckled petal on its flowers. These are more common along sandy washes in southern parts of the Sonoran Desert.
Although Palo Verdes have thousands of tiny leaves (as anyone who has one planted near a pool well knows!), the bright green bark takes care of about 75% of the photosynthesis for the tree, allowing them to endure years of severe drought when leaves are an expensive luxury. During seasons of drought and cold, most of the leaves are dropped to conserve moisture.
No matter what sort of winter rains or not have blessed the land, Palo Verdes are reliable bloomers during late spring, creating drifts of dried flowers along trails and roadsides. If you aren’t spooked by bees, sitting under a blooming Palo Verde is a multi-sensory treat. The golden canopy hums with bees, bathing you in yellow light and the sweet scent of nectar. Every spring I take my kids on a walk to visit the “gold room” of a blooming Palo Verde. There, looking up through green branches to the blue sky is another reminder why we love our neighborhood and its big backyard.
Since May 2005, I have written a natural history column for a neighborhood newsletter published by Jennifer Moore called "Our Big Backyard: Natural History of the Deem Hills," and since 2010, "A Suburban Naturalist."All of these columns are reproduced here. Deem Hills is a City of Phoenix Desert Preserve located just north of Happy Valley Road in north central Phoenix, and just west of I-17. The Preserve and adjacent hills comprise over 900 acres of open space with several miles of hiking trails. For more perspectives from the Deem Hills and suburban Phoenix, also check out my companion blog, Kat Tracks.
As a naturalist with a special interest in botany and plant ecology, some of my greatest passions are to explore, photograph and write about native plants. If I can spark an awareness or interest in natural history in others along the way, that is my greatest reward.