Native to seasonal washes across the American Southwest and northern Mexico, the desert willow (Chilopsis linearis) is a fast growing deciduous tree. Although its wispy branches and narrow leaves resemble those of a willow, this plant is more closely related to catalpa trees and trumpet creeper vines. Desert willow produces showy pink with yellow throated flowers most heavily in late spring. It is hardy to 0 to -5 degrees F and demands perfectly drained soils in regions that receive no more than 30 inches of rainfall annually.
Desert willow's leaves are long and narrow. They range in size from 1/2 to 3 inches long and only 1/4 to 1/2 inch wide, according to the Pima County Master Gardeners in Tucson, Arizona. The Lady Bird Johnson Wildflower Center in Austin, Texas, notes potentially larger sizes: 4 to 12 inches long and 1/3 inch wide.
Heavy fall frosts and winter cold causes the tips of the leaves to brown. With extended exposure to subfreezing temperatures, all leaves drop off the tree. New leaves emerge in spring.
Each desert willow leaf is a light, bright emerald green in color. The longer the leaf blade becomes, the more "weeping" in form it looks when dangling from the thin branches. The Lady Bird Johnson Wildflower Center notes the vein pattern in each blade is pinnate (branching like a feather) or parallel and may vary among trees. The surface is smooth and hairless and there are no teeth on the edges.
The leaves are arranged in a "sub-opposite" pattern on the twigs. This pattern is a frustrating intermediate between an alternating pattern and an opposite pattern. On some branches or groups of leaves an alternate arrangement is prominent, while it other parts of the stem they tend to look certainly opposite.
From late fall to early spring, when no leaves may be present on the desert willow tree, identification centers around the young twigs. Look for many prominent, bright white spots (lenticels) that contrast the darker brown, thin bark. Overall, the tree has a leaning twisted form with open branching. Persistent light brown slender seed pods (6 to 10 inches long) dangle from the branches, too. This tree truly looks dead when fully dormant in winter attests the Las Pilitas Nursery, a purveyor of native plants in Santa Margarita, California.