Parkinsonia is the name of a genus of flowering plants in the Fabaceae pea family. It was named in honor the 16th century English botanist John Parkinson. Twelve species of large shrubs or small trees, native to dry and arid regions of Africa and the Americas, fall under the genus Parkinsonia. Hardy by nature, the plants can pose a substantial risk to non-native regions, such as the semi-desert areas of Australia where they are considered weeds. They can also, however, act as a supplemental dietary source for rural groups in drought-stricken areas.
The 13 Parkinsonia species are described as small prickly trees or large shrubs, ranging in height from about 16-40 feet (about 5-12 m). They possess an elaborate surface root system and a deep taproot. Their leaves are thin and pale green with a feathery appearance.
These plants' flowers vary in color from yellow to white, but all of them possess five petals. Perhaps the most distinctive feature of plants in the Parkinsonia genus are their green trunks. In fact, most American species are referred to by the common name "palo verde," which means "green stick" in Spanish.
Although the plants of the Parkinsonia genus are native to three continents — North America, South America and Africa — they have spread far beyond their native borders. The hardy plants are capable of weathering extreme heat and drought. Their seeds possess thick outer shells and can remain viable underground for years before ever germinating. This can make any Parkinsonia species imposing competition when introduced to foreign soil, as in the case of Australia.
Settlers introduced Parkinsonia to Australia during the latter half of the 19th century. Originally intended as an ornamental shade tree to be planted around settlements, the flowering plants flourished in the semi-dry climate of Northern Australia. They are now considered a significant exotic weed capable of impeding local plant and animal welfare. The government of Australia has a program in place for controlling the future spread of the plants.
Several species of Parkinsonia have historically been used as sustenance for humans and livestock. The foothill palo verde, for example, native to northwestern Mexico, was once prized by the indigenous Seri people who ground the seeds into flower, boiled the pods as a vegetable and enjoyed the sweet fruit pulp as a treat. In dry areas and areas plagued with drought, the leaves and seeds of another North American species, the Jerusalem thorn, are still fed to sheep and goats.