The Jerusalam thorn produces showy clusters of of brilliant yellow and orange flowers beginning in late Spring. Click to download a large version (800x600) of this image.
Jerusalem thorn is a small tree growing to 25 ft (7.6 m) tall with a short trunk and a graceful, spreading, sometimes weeping, crown to 20 ft (6.1 m) wide. The slender branches and twigs have green bark, and are armed with stout spines up to 1 in (2.5 cm) long. Jerusalem thorn has peculiar straplike, twice compound leaves that look like long, feathery streamers. Each leaf is modified into 2 or 4 strips about 10-16 in (25.4-40.6 cm) long and less than an 1 in (2.5 cm) wide. Each strip has 22-30 pairs of tiny opposing leaflets less than 0.33 in (0.8 cm) long. The leaves appear shortly after rain, they fold up at night, and usually within a few days the tiny leaflets drop off, leaving the persistent rachises (midribs) to flutter like streamers in the wind. Eventually these fall off too, and accumulate like pine needles beneath the tree. A spectacular display of clustered pealike flowers in spring makes the whole tree look like a giant yellow bouquet. The brown pods are about 3-4 in (7.6-10.2 cm) long and constricted between the seeds.
There are five species in the genus Parkinsonia: four in North and South America and one in South Africa. Jerusalem thorn is native to desert grasslands and canyons in Mexico and the SW US where it often grows in association with mesquite (Prosopis spp.). It is grown as an ornamental in tropical and subtropical climates and has escaped cultivation and established in Florida, California, the West Indies, and in Australia where it is regarded as one of the most troublesome invasive weeds in the Northern Territories. Jerusalem thorn has been used to revegetate desertified regions in Africa and Pakistan.
Jerusalem thorn does well on sandy or gravelly soils, and is tolerant of alkaline and chalky soils. It grows fast and has few pests.
Light: Full sun. Moisture: Drought tolerant. Survives in regions that receive less than 12 in (30.5 in) of annual rainfall.
Hardiness: USDA Zones 8 - 11. Thrives in heat. Is damaged at temperatures below 18ºF (-7.8ºC). Propagation: By seed. Jerusalem thorn produces two kinds of seeds within the same pod. About 25% of the light brown seeds germinate readily. The rest of the light brown seeds and all of the dark brown seeds have hard seed coats which must be scarified before they will germinate.
The Jerusalem thorn's wispy foliage shimmers in a green haze when backlit by sunlight.
Jerusalem thorn is well suited to informal landscapes. Use it in a cactus and succulent garden and let its lacy foliage and slender twigs contrast with the solid blocky shapes of the succulents. Unaffected by heat, Jerusalem thorn makes a fine street or patio tree and provides a delicate, filtered shade.
Jerusalem thorn is highly adapted to life in the desert. It has largely done away with leaves that lose water through evaporation and transpiration, producing its food instead within the photosynthetic tissue of the bark.
Native Americans harvested the seeds of Jerusalem thorn which they sun dried for storage and parched over dry heat before eating.