The Western Soapberry tree (Sapindus saponaria var. drummondii) is a slow-growing deciduous tree with a dense canopy of dark green compound leaves. It occurs throughout the southern Great Plains, extending into eastern Arizona and the Mogollon Rim. In Arizona it typically grows 15 to 20 feet high, but can get up to 50 feet high in deep soil. Varieties of soapberry are also native to Hawaii, Mexico, South America, New Caledonia, and Africa.
The tree produces copious clusters of tiny white flowers in the spring and early summer. These flowers attract hundreds of pepsis wasps and bees. (see Pepsis wasps have the most painful sting and Desert Bees ) You can see two of these trees at the Arizona-Sonora Desert Museum near the Prairie Dog exhibit. According to ASDM, the Western Soapberry is the larval food plant for the Soapberry Hairstreak butterfly. (See butterfly images) See more photos of the flowers, fruit and seeds here.
Upon pollination, the flowers turn into a whitish-yellow, grape-sized fruit which is both poisonous and unpalatable. The fruit turns darker, golden to red, with age. The fruit produces a single large seed.
The fruit is poisonous because it contains saponin, a compound that tastes like soap and can be used as soap when mixed with water. This mixture was also used as floor wax and varnish according to the US Forest Service. The mixture can cause dermatitis in some people.
Native people made necklaces and buttons from the round dark brown seeds.
According to TexasBeyondHistory:
More than one group found the wood to be useful for making arrows. The Comanches fashioned arrows from the stems of western soapberry. The Papago used the wood of soapberry to make the foreshaft of their arrows.
The bark was peeled off of slender green soapberry stems, which then were straightened and dried. They arrow maker then split the tip of the dried shaft, inserted the small stone arrow point, and tied it with wet sinew. The account notes that a gum from brittlebush (Encelia farinosa) was utilized to cement the tip to the shaft; however, brittlebush does not grow on the Edwards Plateau or eastern Chihuahuan Desert. We do not know what type of gum may have been used in our region. The arrow artisan would make the main arrow shaft from soaptree yucca (Yucca elata) or from common reed (Phragmites communis). Common reed grows throughout the area, but on the Edwards Plateau, Thompson yucca flower stalks would have been used instead of the soaptree, which grows further west in the Trans-Pecos region. A hole two-inches deep was hollowed into the end of the arrow shaft so that the foreshaft (fashioned of soapberry) could be inserted. Once inserted, sinew was wound tightly around the entire length of the hollowed out area.
The Western varietal name for this plant, drummondii, is, according to the Lady Bird Johnson Wildflower Center, “named for Thomas Drummond, (ca. 1790-1835), naturalist, born in Scotland, around 1790. In 1830 he made a trip to America to collect specimens from the western and southern United States. In March, 1833, he arrived at Velasco, Texas to begin his collecting work in that area. He spent twenty-one months working the area between Galveston Island and the Edwards Plateau, especially along the Brazos, Colorado, and Guadalupe rivers. His collections were the first made in Texas that were extensively distributed among the museums and scientific institutions of the world. He collected 750 species of plants and 150 specimens of birds. Drummond had hoped to make a complete botanical survey of Texas, but he died in Havana, Cuba, in 1835, while making a collecting tour of that island.”