Carnegiea gigantea, Giant Saguaro

Southwest Desert Flora

Home to the plants of the Sonoran, Chihuahuan and Mojave Deserts

Cirsium ochrocentrum, Yellowspine Thistle

Psorothamnus spinosus, Smoketree

Smoketree or Indigobush has dark purple, violet or indigo-blue pea-like flowers that explode with color in late spring. Psorothamnus spinosus Smoketree flowers are easily recognized because the sepals have visible glands dotted on the calyx. Smoketree blooms from April to June in Arizona; slightly later in California; June to July and again in October and November with sufficient rainfall. Psorothamnus spinosus Smoketree is a native desert tree or large shrub that prefers sandy and gravelly washes. With small leaves the trunk, stems and branches produce food by photosynthesis. Psorothamnus spinosus Smoketree; The common name Smoketree is a reference to the normally gray appearance of the tree, which, in late spring completely changes to a blast of violet or indigo-blue flowers. Stems and branches have brown gland dots ending in sharp spines. Psorothamnus spinosus

Scientific Name: Psorothamnus spinosus
Common Name: Smoketree

Also Called: Indigobush, Smoke Thorn, Smoke Tree, Smokethorn Dalea, Smokethorn ( ES: Palo de Humo, Palo Cenizo, Corona de Cristo, Mangle)

Family: Fabaceae or Leguminosae Family

Synonyms: (Dalea spinosa)

Status: Native

Duration: Perennial.

Size: Up to 25 feet (7.6 m) or more.

Growth Form: Smoketree is a shrub or subshrub and rarely a tree, the trunk is short, crooked and intricately branched with smoky gray or silvery branches, all with spiny twigs throughout, similar to the Paloverde the green trunk, stems and branches produce food through photosynthesis.

Leaves: Smoketree may be leafless most of the year with the leaves falling off early in the spring, thus the ability to photosynthesize, the few leaves are green or silvery in color; the silvery or smoky colored leaves, from a distance give a hazy appearance and thus the common name "Smoketree".

Flower Color: Smoketree has showy dark purple, violet or indigo-blue pea-like flowers, the fruit is an egg shaped pod with 1 or 2 seeds.

Flowering Season: April to June, slightly later in California, June to July and October to November.

Elevation: 1,500 feet (457 m) or lower; below 1,200 feet (366 m) in California.

Habitat Preferences: Desert sandy washes.

Recorded Range: In the United States Smoketree is found in the southwest in AZ, CA and NV. In Arizona is occurs in the west, central and southern parts of the state, in southeast California and southeast Nevada. It is also native to Baja California and northwest Mexico.

North America & US County Distribution Map for Psorothamnus spinosus.

U.S. Weed Information: Unknown
Invasive/Noxious Weed Information: Unknown
Wetland Indicator: Unknown
Threatened/Endangered Information: Unknown

Genus Information: In North America, USDA Plants Database lists 8 species and accepted taxa overall for Psorothamnus. Worldwide, World Flora Online includes 19 accepted species names and a further 15 scientific names of infraspecific rank for the genus.

The genus Psorothamnus was published in 1919 by Per Axel Rydberg, (1860-1931).

In the Southwestern United States: Arizona has 7 species of Psorothamnus, California has 6 species, Nevada has 5 species, New Mexico and Texas each have 1 species and Utah has 4 species. Data approximate, subject to revision.

Comments: 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.

The type species was collected by William Hemsley Emory, (1811-1887) along the Gila River.

In Southwest Desert Flora also see Schott's Dalea, Psorothamnus schottii.

Importance to Wildlife, Birds and Livestock
Smoketree, Psorothamnus spinosus has attractive flowers, the flowers and their seeds may be visited by hummingbirds and/or small mammals including rodents and granivorous birds in search of nectar or food.

Beneficial Value to Butterflies, Honey Bees and Insects
Smoketree, Psorothamnus spinosus has attractive flowers, the flowers and their plants may be visited by butterflies, moths, flies, honeybees, Native Bees and other insects in search of food and nectar.

****Special Value to Native Bees****
According to The Xerces Society for Invertebrate Conservation or other source, Smoketree, Psorothamnus spinosa, is recognized by pollination ecologists as attracting large numbers of native bees, specifically Bumblebees (Bombus spp.). Click here for more information on their Pollinator Conservation Program.

The genus “Psorothamnus” (Psorotham'nus:) is from the Greek psoros, "mangy, scabby," and thamnos, "bush," thus "scabshrub."

The genus Psorothamnus was published in 1919 by Per Axel Rydberg, (1860-1931).

The species epithet spinosus (spinos'us:) is from Latin for "thorny."

The original taxon Dalea spinosus was first described in 1854 by Asa Gray, (1810-1888), and later as Psorothamnus spinosus in 1977, by Rupert Charles Barneby, (1911-2000).

Ethnobotany - Native American Ethnobotany; University of Michigan - Dearborn

Date Profile Completed: 09/07/2015, updated 02/23/2022
References and additional information:
Arizona Flora, Kearney, Thomas H., Peebles, Robert H., 1960, University of California Press, Berkley and Los Angeles, California, as Dalea spinosa.; Department of Agriculture, Natural Resources Conservation Service on-line database and USGS ITIS search; accessed on-line; 02/22, 23/2022.
World Flora Online; A Project of the World Flora Online Consortium; An Online Flora of All Known Plants - (accessed on-line; 02/22/2022)
Rhodes, Suzanne, June Beasley and Tina Ayers. 2011.Fabaceae. CANOTIA 7: 1-13. Journal of the Arizona-Nevada Academy of Science; Volume 7.; accessed on-line 02/22/2022.
The Jepson Desert Manual; 2002; Baldwin, Bruce G., et. al.; The Jepson Desert Manual: Vascular Plants of Southeastern California; p 325; Univ. of California Press, Berkeley and Los Angeles, California
Martin F. Wojciechowski & Duane Isely 2012, Psorothamnus spinosus, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on February 22, 2022.
Native Plant Information Network, NPIN (2013). Published on the Internet [accessed: 02/22/2022, updated 02/14/2017]. Lady Bird Johnson Wildflower Center at The University of Texas, Austin, TX.
Wikipedia contributors. "Psorothamnus spinosus." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 16 Dec. 2021. Web. 22 Feb. 2022.
SEINet synonyms, scientific names, geographic locations, general information.
Etymology: Michael L. Charters California Plant Names: Latin and Greek Meanings and Derivations; A Dictionary of Botanical and Biographical Etymology - (accessed on-line; 02/22/2022)
IPNI (2020). International Plant Names Index. Published on the Internet, The Royal Botanic Gardens, Kew, Harvard University Herbaria & Libraries and Australian National Botanic Gardens. [Retrieved on-line; 22 and 23, February 2022].