Fraxinus anomala aka Utah Ash

Fraxinus anomala is a deciduous shrub or small tree. Its common names are singleleaf ash and dwarf ash. It belongs to the olive family, Oleaceae. Kew places its native range in the western United States, reaching New Mexico. Oregon State gives a broader range that includes northern Mexico. The species is not native to Oregon or Britain. Unlike most ashes, it usually bears simple leaves. Its name refers to this unusual leaf form.

Plants grow about 5–20 feet (1.5–6 m) tall. The tree form has a rounded crown and crooked trunk. Other plants grow upright, often with more than one trunk. The trunks stay short beneath the branches. Young bark is smooth and light brown. With age, it turns darker and forms narrow, rough ridges. Shallow cracks divide the thin bark into small scales. The stout twigs have four angles and an orange-brown shade. Lines or wings run along their sides. Darker buds have a rough surface. Slightly raised leaf scars form crescent shapes below them.

Leaves grow in opposite pairs along the stems. Most have one blade, though some have two or three leaflets. The blades range from oval to almost round. They measure about 1.5–2 inches (4–5 cm) long. Their width is close to their length. The upper face is smooth and green to dark green. The underside has a paler shade. Leaves feel thin yet somewhat leathery. Their edges may be smooth or have slight, wavy teeth. Leaves with several leaflets have smaller individual blades.

Small, pale yellow-green flowers grow in clusters on older shoots. They open before the leaves or as leaves emerge. One plant carries both male and female flowers. The flowers are not showy. Clusters of papery samaras follow and ripen from mid- to late summer. Each fruit has one straight wing extending to the seed base. Reported fruit lengths reach about one inch (2.5 cm).

Oregon State recommends sun and lists hardiness to USDA Zone 4. Its species page also carries an emerald ash borer warning. The larvae feed beneath ash bark and disrupt water and nutrient flow. This damage can kill affected trees.