Palo azul is the more common name for Eysenhardtia polystachya, a shrub or tree of the Fabiaceae or legume family, which is native to northern and central Mexico and Arizona. It is deciduous and grows from 3 to 20 feet, depending on location. The young branches are covered with fine hairs and the foliage features compound, paired leaflets in groups of two to four. In spring 3-inch flower spikes appear with clusters of fragrant, white blossoms, which are followed by 3-inch long seedpods. Palo azul is of medicinal and ethnobotanical, or cultural, importance.
Palo azul has been known for centuries. Sixteenth century Mexican scholar, Martin de la Cruz, described palo azul as a hiccup treatment. In the same century, scholar Francisco Hernandez prescribed the plant for a number of inflammatory and digestive ailments. Still another authority, 18th century writer, Juan de Esteyneffer, suggested that palo azul be used as a diuretic and remedy for kidney disease. In the 19th century, writers for the Mexican Society of Natural History described the plant's traditional use as a diuretic.
Palo azul is also known as kidneywood, palo dulce and palo santo. Palo azul means "blue stick" in Spanish, possibly as a reference to the blue dye obtained from its wood. Palo dulce means "sweet stick" and palo santo translates as "holy stick." The name kidneywood refers to the plant's purported medicinal properties. Other Eysenhardtia species are also known as kidneywood.
Traditional Medicinal Use
Palo azul was used as a traditional Mexican remedy for kidney problems, such as bloody urine and kidney stones. It was consumed in the form of a tea brewed from the plant's leaves and stems.The same tea was used to prevent miscarriages.The flowers of palo azul were combined with other flowers, including elder flowers, to make an extract given to children to treat diarrhea. A bark infusion was sometimes used for contraception. Preparations made from palo azul plant parts were taken internally to treat diabetes and applied externally to cleanse wounds and wash out the eyes.
Palo azul is an excellent landscape plant, especially for xeriscape or dry garden situations. It can be propagated by seeds or softwood cuttings that are collected in the fall. The trees occur naturally in dry, rocky soil and should be planted in locations with excellent drainage. Water until established; afterwards, minimal irrigation should be necessary. For xeriscape landscaping, group palo azul trees with other plants that have low water needs.
Members of the Eysenhardtia or kidneywood family, have been used as a food source for browsing cattle, sheep and goats. They are also attractive to deer. The fragrant white flowers are an excellent source of nectar for honey bees and attract butterflies as well. Kidneywood is also the larval food of the dogface butterfly.
- United States Department of Agriculture: Germplasm Resources Information Network: Eysenhardtia polystachya
- Xeriscape Landscaping Plants for the Arizona Desert Environment
- "Native Woody Plants of the United States"; William Van Dersal; 2007
- Plant Atlas of Traditional Medicine Mexicana
- The University of Texas at Austin: Native Plant Database: Eysenhardtia texana
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