Jerusalem Thorn, Mexican Palo Verde

Known as both the Mexican Palo Verde and the Jerusalem Thorn, this small, fast-growing tree is native to the southwestern United States and Mexico. It was one of the first ornamental trees to be introduced into Saudi Arabia. A rounded, graceful tree, usually with a multi-stemmed, green trunk, drooping branches and slender twigs, it grows up to 8 metres high and 5 metres wide. The foliage is short-lived under desert conditions, but when the trees become leafless, the petioles of the leaves remain like silky needles. They are bordered by two rows of 25–30 tiny oval leaflets; during drought, the tree becomes deciduous. The branches have sharp spines 7–12 mm long. Sporadically blooming, loose clusters of fragrant, golden-yellow flowers with an orange-reddish coloured throat, make a striking display in spring and are followed by slender bean pods up to 15 cm long. P. aculeata prefers well-drained, sandy and alkaline, alluvial soils. In full sun, it will need watering until it becomes established. It is a very hardy tree, and tolerant of frost, wind, salinity and drought. Propagation is by seed. It is prone to attacks by red spider mites and mealybugs. Some countries have registered invasion problems: it is now a serious, widespread weed in Australia. Extremely attractive for landscape design, its graceful form has a residential scale and provides filtered shade: it is also suitable as a street tree and for screening. Maintenance is moderate: leaf litter will require removal. Pruning is necessary to create the desired shape.