Single-leaf ash

Description

Fraxinus anomala is a species of ash tree known by the common name single-leaf ash. It is native to the southwestern United States and northern Mexico, where it grows in a number of habitats including desert scrub and chaparral. It is unusual in the genus in that some (though not all) specimens have simple leaves instead of the pinnate leaves more characteristic of the group. Fraxinus anomala is a deciduous shrub or small tree approaching maximum heights of five to six meters. The leaf may be simple or it may be compound, composed of up to five leaflets which look like individual leaves. Each leaflet is oval-shaped to round and may have teeth along the edges. The nondescript brownish flowers lack petals. The fruit is a flat samara up to two centimeters long and one wide, green when young and tan to brown when mature. The samaras hang in bunches. In Arizona, singleleaf ash is found along the Arizona transition zone of the Mogollon Rim. In northern Arizona's Grand Canyon, the range extends down the main canyons from southern and southeastern Utah, its major range area, where the Canyon Lands also show the range entering upper reaches of river basins flowing from western Colorado – Colorado and Dolores Rivers; also the shorter Yellowjacket and McElmo Rivers in Colorado's extreme southwest. In the Mojave Desert of California it is found in the sky island chaparral and woodland habitats. Minor locales also occur in southern Nevada and southern Wyoming. The leaves are opposite (rarely in whorls of three), and mostly pinnately compound, though simple in a few species. The seeds, popularly known as "keys" or "helicopter seeds", are a type of fruit known as a samara. Some Fraxinus species are dioecious, having male and female flowers on separate plants but sex in ash is expressed as a continuum between male and female individuals, dominated by unisexual trees. With age, ash may change their sexual function from predominantly male and hermaphrodite towards femaleness; if grown as an ornamental and both sexes are present, ashes can cause a considerable litter problem with their seeds. Rowans or mountain ashes have leaves and buds superficially similar to those of true ashes, but belong to the unrelated genus Sorbus in the rose family.