Desert Kidneywood
Eysenhardtia orthocarpa

Family: Fabaceae

OTHER COMMON NAMES
Spanish: palo cuate, palo dulce

CHARACTERISTICS
This is an upright deciduous large shrub or small tree, reaching up to 20’ tall (though usually much shorter in our region), and usually about 10’ wide. Nectar-rich, sweetly fragrant flowers emerge in April-September. Flowers are followed by one-seeded, flat pods that are unusual for a legume (orthocarpa means strange fruit). Finely divided leaves have sunk-in (punctate) glands on the bottoms, and when crushed the leaves are said to smell like tangerine.

Photo by Dan Beckman on iNaturalist

LANDSCAPE USE
Screening shrub or small tree.

GROWING CONDITIONS
AN EXPLANAITION OF TERMS USED

SUN full sun, can tolerate part sun when young
WATER moderate to low, slower growing with less water, can live on rainfall when established
SOIL tolerant but good drainage is important
HARDINESS hardy to single digits °F
BASIN middle to high
CONTAINER does ok but won’t reach potential size
NUTRITION low
MAINTENANCE very little

ECOLOGY
Sweet smelling flowers attract loads of butterflies, bees, and other insects. This is a larval food plant for the Arizona Hairstreak (Erora quaderna), the marine blue (Leptotes marina), the Ceraunus Blue (Hemiargus ceraunus), and the Gray Hairstreak (Strymon melinus). Seeds provide for some granivorous birds. The upright nature of this tree provides safe nesting and perching habitat for birds.

ETHNOBOTANY
The wood chips and or leafy branches can be steeped or boiled in water to make tea. This tea can be used for enjoyment and is sometimes used in remedies for kidney and bladder ailments, hence the common name.

When the wood chips are steeped in cold water for a few hours, they confer a blue hue to the water (hence one of its popular names in Spanish, palo azul or “blue stick”). This color can later change to red or amber, according to the incidence of the light. The Spanish physicians first recorded the intense blue fluorescence of kidney wood tea in the sixteenth century. This interesting phenomenon is due to a novel four-ringed chemical compound known as tetrahydromethanobenzofuro[2,3-d]oxacine, which is not found in the intact plant, but rather is the end product of an unusual spontaneous oxidation involving some of the plant’s natural compounds known as flavonoids.

The wood is sturdy and occasionally used for various projects.

NATURAL DISTRIBUTION
Found on rocky and gravelly ridges and along watercourses, often along water courses below 5,500 ft. in southeastern Arizona, southwestern New Mexico; south into central Mexico.

TAXONOMY AND NAME
This species is in the Fabaceae (Legume family). There are 13 accepted species of Eysenhardtia in the United States, Mexico, and Central America.
The genus “Eysenhardtia” is named for Karl Wilhelm Eysenhardt (Carolus Guilielmus Eysenhardt) (1794-1825), German (Berlin) physician, zoologist, naturalist and botany professor. The species epithet “orthocarpa” is from the Greek orthos, meaning "straight," and karpos, which means "fruit," thus "straight fruit, referencing the relative shape of the pod." The common name kidneywood refers to its medicinal use for kidneys and urinal issues.
A similar species, the Texas kidneywood (Eysenhardtia texana) is a somewhat smaller and slightly hardier to the cold, and is sometimes available in the trade. Another species, Eysenhardtia polystachya is a more tropical version of this species, and considered the same species by some authors.

Eysenhardtia orthocarpa on iNaturalist
Eysenhardtia orthocarpa on SEINET