Desert Smoketree
Psorothamnus spinosus
Family: Fabaceae
OTHER COMMON NAMES
Smokethorn
Spanish: palo de humo, palo cenizo, corona de cristo, mangle
CHARACTERISTICS
This is an unusual, spinescent tree which often defies what we consider as a tree, though it often has a trunk and a canopy. This almost leafless, spiny tree has aromatic foliage and often an irregular canopy and reached about 20’ tall eventually. Dark purple to blue flowers appear in April-June followed by legume seed pods. The foliage is incredibly aromatic. The common name "Smoketree" is a reference to a smoky look from a distance due to the normally gray appearance of the tree, which, in spring, completely changes to a blast of violet or indigo-blue flowers.
Photo by siempreviva on iNaturalist
Psorothamnus spinosus on SEINET
LANDSCAPE USE
Specialty accent plant
GROWING CONDITIONS
AN EXPLANAITION OF TERMS USED
SUN full sun
WATER low, can live on rainfall when established
SOIL prefers sandy or rocky soil, good drainage is a must
HARDINESS hardy to about 20-25°F, sustains damage in the lower 20s
BASIN middle to high zone
CONTAINER not recommended
NUTRITION low
MAINTENANCE very little, older branches naturally durn brown and die, do not worry about them
ECOLOGY
Important nectar plant—used by hummingbirds, bees, and more. Various granivorous birds and mammals consume the seeds. This is a larval host for the Burns' buckmoth (Hemileuca burnsi), and the Ceraunus Blue (Hemiargus ceraunus). A very cool parasitic plant lives on species of Psorothamnus, Thurber’s stemsucker (Pilostyles thurberi), which lives inside the tissue of the host until it flowers. If you see brown or pinkish flowers on this plant (the flowers are usually purple for smoke trees) then you might be looking at this cool parasitic plant.
ETHNOBOTANY
The genus has a long history of medicinal use.
NATURAL DISTRIBUTION
Most often found in sandy desert washes and roadsides in Arizona, California and Nevada, and in neighboring Sonora and Baja California—so, found in both the Mojave and Sonoran Deserts.
TAXONOMY AND NAME
This species is in the Fabaceae, the bean family. There are 10 species of Psorothamnus native to the southwestern United States and northern Mexico.
Formerly known as Dalea spinosa.
The genus “Psorothamnus” is derived from the Greek psoros, "mangy, scabby," and thamnos, "bush," thus "scabshrub” referring to the glandular nature of the genus. The species epithet “spinosus” is from Latin for "thorny." The former genus, Dalea, honors English apothecary Samuel Dale (1659–1739).
Desert Smoketree looks like smoke from the distance. The newer, fresh, silvery stems grow atop the older, dead, tannish branches. Photo by Irene, iNaturalist
A closeup of the individual flower, showing the prominent glands on the sepals of the flowers. Photo by Rod, iNaturalist
The spinescent, silvery stems are very aromatic. Photo by quandary, iNaturalist
Close inspection of the stems reveals the glandular nature of the plant which lends to its aromatic nature. Photo by Tony Iwane, iNaturalist
Flowers of the parasitic plant, Thurber’s stemsucker (Pilostyles thurberi). Photo by Carla Hoegen, iNaturalist