Semi-desert, foothills. Woodlands, openings, rocks, canyons. Spring.
Hidden Valley Trail, Utah, May 10, 2007.

Single Leaf Ash is, as its specific epithet indicates, an anomaly.  It is the only Ash with single, not compound, leaves, i.e., its leaves are whole, having no divisions.  The tree has multiple trunks, is typically 8-14 feet tall, and is found near washes and in rocky areas.

The tree pictured has young spring leaves that will grow and fill in the airy spaces.  Because this tree is growing in a canyon bottom near a small stream, it is less branched than most Single Leaf Ash trees and does not have the dead branches common to most Single Leaf Ash.  This tree is about twelve feet tall with the largest of its multiple trunks over three inches in diameter.

Semi-desert, foothills. Woodlands, openings, rocks, canyons. Spring.
Near McElmo Canyon, May 14, 2001.

Cluster of tiny, petal-less, and short-lived flowers change from yellow to light greenish-yellow.

Leaf margins can be almost smooth (as in the two background leaves), very slightly serrated (as in the foreground leaf) or finely and sharply serrated (as in the leaves shown in the picture below).

Semi-desert, foothills. Woodlands, openings, rocks, canyons. Spring.
Hunter Canyon, Utah, May 3, 2005.

Green then yellow then buff winged seed pods (samaras) follow the profusion of yellow flowers.

Semi-desert, foothills. Woodlands, openings, rocks, canyons. Spring.
Canyonlands National Park, Utah, November 1, 2005.

Fall colors are golden yellows.

Semi-desert, foothills. Woodlands, openings, rocks, canyons. Spring.
Canyons of the Ancients National Monument, March 14, 2008.

Single Leaf Ash is deciduous and is easily recognized in the winter by its dark bark, stubby twigs, and vertical growth pattern.

Semi-desert, foothills. Woodlands, openings, rocks, canyons. Spring.
Negro Bill Canyon, Utah, April 14, 2008.

Bark on a mature Single Leaf Ash is dark gray and flaky.