State tree of Arizona; found in the Sonoran desert, in southeastern California, central and southwestern Arizona, and in western Sonora, Mexico.

The name palo verde comes from the Spanish for green wood or stick; species of this tree have smooth greenish trunks and branches, through which they are able to photosynthesize. Two species are prevalent in the American Southwest; the foothill palo verde and the blue palo verde . Both are relatively short multi-trunked trees with small leaves; although one source names them deciduous, another claims the palo verde is not a proper tree at all, but a legume, closely related to alfalfa.

Both species produce seed pods which are eaten by an assortment of desert animals, and both produce an abundance of five-petaled yellow blossoms during their short flowering seasons (April or May). Palo verdes drop their leaves, stems, and branches to combat drought, and also drop their leaves when the temperatures drop in autumn. Both are of interest to gardeners and landscapers and are planted in urban areas, as well as their natural desert habitat.

Palo verdes act as nurse plants for young saguaro cacti—their leaves and branches serve as a canopy to protect the slower growing cactus. When flowering, they attract a myriad of pollinators including beetles and flies, as well as about 20 varieties of bees. Their branches provide nesting areas for a variety of desert birds, and feral burros, bighorn sheep, javelina, mule deer, jackrabbits, and other small mammals all browse palo verdes. Wood boring beetles make dead limbs or branches their home, as do bees.

Foothill palo verde (Cercidium microphyllum)

Also known as the littleleaf or yellow palo verde, this tree usually reaches heights of only 20 feet; its bark is yellowish green and blooms are light yellow and white in color; seeds are the size of lentils and can be eaten by humans. Foothill palo verde grow in uplands and require less water than blue palo verde; this variety often lives well past the century mark, sometimes reaching the ripe old age of 400 years.

Blue palo verde (Cercidium floridum)

As suggested by the name, this tree’s twigs, young branches, and leaves are bluish green. This variety grows in washes, requires more water, grows faster than the foothill palo verde, reaches heights of 40 feet, and has larger leaves and brighter (yellow) flowers. Seed pods are larger, thicker, and flatter. Blue palo verde tend to live only 20-40 years.

Sources: David B. Williams, Palo Verde Tree, 5/23/02 also 5/23/02 and 5/24/02 as well as 5/24/02


Of related interest:

Angiosperm Witness for the Prosecution

For the first time a murderer has been convicted on DNA evidence obtained from a plant. The case was described in the PBS TV series, Scientific American Frontiers, amiably hosted by a continually bemused Alan Alda, the perfect foil for the scientists he interviews. The murder of a young woman occurred in Phoenix, Arizona, and the finding of a pager at the scene of the crime lead the police to a prime suspect in the case. He admitted picking up the victim, but claimed she had robbed him of his wallet and pager. The forensic squad examined the suspect's pickup truck and among the bits of evidence collected were pods later identified as the fruits of palo verde (Cercidium spp.). One detective went back to the murder scene and found several palo verde trees, one of which showed some damage that could have been caused by a vehicle. The detective's superior officer innocently suggested the possibility of linking the fruits and the tree by using DNA comparison, not realizing that this had never been done before. Several researchers were contacted before a geneticist at the University of Arizona in Tucson agreed to take on the case. Of course, the first crucial study was to establish evidence that would stand up in court on whether individual plants (especially the palo verde trees) have unique patterns of DNA. A preliminary study on samples from different trees from the murder scene and elsewhere quickly established that each palo verde tree was unique in its DNA pattern. It was then a simple matter to link the pods from the suspect's truck to the damaged tree at the murder scene and obtain a conviction.*

*WNED-TV (PBS - Buffalo, N.Y.), January 19, 1994 , quoted on

Is this a hoot or what? The trees are absolutely lovely, by the way. Find a picture on the web if you're not familiar (check the sites listed above)...

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