The Genus Psorothamnus
Smokebush
Family: Fabaceae
This is a wonderful genus of about 9 species of shrubs, occasionally trees, native to the southwestern United States and Mexico in arid regions. They were previously placed in the genus Dalea and thus sometimes they are called indigo bushes. But their more extreme xeric nature sets them apart from the Dalea species you might know. Most Psorothamnus species are rare in cultivation. They aren’t fond of containers.
All smokebushes (smoke trees) require very good drainage and aren’t tolerant of tight, clay soils. They also prefer full sun or even reflective heat. Once established plants have very low water requirements, though irrigation during their growth spurts (like during monsoon) makes them grow faster. Most Psorothamnus are surprisingly cold hardy too.
Photo of Schott's Indigobush (Psorothamnus schottii) by Markc666 on iNaturalist
These are normally spring or summer blooming plants with flowers that attract lots of bees, butterflies, and other species. Larval food plant for the painted lady (Vanessa cardui) and ceranus blue (Hemiargus ceraunus) as well as the moth Hemileuca burnsi.
Smokebushes host a cool parasitic plant!
Smokebushes are also the host for a fascinating parasitic plant called the Thurber's Stemsucker Pilostyles thurberi. This plant lives most of its live inside the stems of Psorothamnus species especially Emory's indigo bush or dyebush (Psorothamnus emoryi) emerging only to bloom and fruit.
This species is found in both the United States and Mexico. It has been recorded from the states of Arizona, California, New Mexico, Nevada, Texas in the United States. In Mexico, this species is found in the state of Baja California, ranging from Mexicali to San Felipe, and in the states of Sonora and Chihuahua. It occurs primarily in open desert scrub, from 100 to 1000 meters in elevation.
Photo by Fred Melgert / Carla Hoegen, iNaturalist
Pilostyles thurberi on SEINET
Mojave indigobush
Psorothamnus arborescens
Despite the species name, this plant almost never gets over 3’ tall. The inflorescence is a long raceme of many flowers with reddish green calyces of sepals and bright purple pealike corollas. The fruit is a glandular legume pod up to a centimeter long containing one seed. The seed pod is the only way to tell the difference between P. arborescens and the very similar species, P. fremontii—the glands on P. fremontii are numerous and tiny with almost no space between them. The glands on P. arborescens are larger and more spaced out.
It is found in the Californian Mojave Desert and Colorado Desert, south into the Sonoran Desert in the Mexican state of Sonora, east past the Sierra Nevada into the Nevada Great Basin Desert, and west into the San Bernardino Mountains of Southern California.
Photo by Max Licher, SEINET
Psorothamnus arborescens on iNaturalist
Dyebush
Psorothamnus emoryi
This is a wide-growing bush, often much wider than tall, though reaching 3-4’ tall sometimes. From fuzzy calices come purple flowers. The flowers turn into single-seeded pods. This plant is spineless.
Found on desert mesas of the southern part of the U.S. states of Arizona and California, and regions of the Mexican state of Baja California.
Photo by Zachary Nielsen, iNaturalist
Psorothamnus emoryi on SEINET
Freemont’s Smokebush
Psorothamnus fremontii
Shrubs growing 3-5’ tall. Purple flowers on long, open racemes. Single-seeded pods follow. The seed pod is the only way to tell the difference between P. arborescens and this species—the glands on P. fremontii are numerous and tiny with almost no space between them. The glands on P. arborescens are larger and more spaced out.
Common to the Southwestern United States and northwest Mexico - in the states of California, Nevada, Utah, and Arizona, Sonora, and Baja California.
Photo by ann2022, iNaturalist
Psorothamnus fremontii on SEINET
Schott's Indigobush Psorothamnus schottii
This species is larger than the other shrubby indigobushes, reaching 6’ tall. Purple flowers on racemes followed by single seeded pods.
Native to the Sonoran Deserts of northern Mexico and adjacent sections of Arizona and the Colorado Desert in California.
Photo by Philip Georgakakos, iNaturalist
Psorothamnus schottii on SEINET
Broom Indigobush
Psorothamnus scoparius
Broom dalea is a small shrub with grey colored branches and a broom-like appearance. Purple flowers and only a few simple leaves appear after rains.
Native to the southwestern United States, particularly sandy areas within New Mexico's Rio Grande valley. It is rarely seen in adjacent states and the northernmost region of Chihuahua, Mexico.
Photo by David Greenberger, iNaturalist
Psorothamnus scoparius on SEINET
Desert Smoketree
Psorothamnus spinosus
Shrubs or small trees reaching 20-25’. Dark purple to blue flowers appear in April-June followed by single-seeded pods.
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. Here is a complete profile of this species in our tree section.
Photo by Keith Godwin, iNaturalist
Psorothamnus spinosus on SEINET