The average person should not let the fact that she has a hard time identifying the leaves of North American ash trees bother her. Even seasoned botanists can struggle with this job, says "Trees of North America," since the ashes have striking similarities in this regard. By keeping in mind some of the aspects of the ash tree, you will enhance your chances of identifying its foliage.
The ash species in North America share three traits concerning their leaves. The trees are deciduous, shedding their foliage before winter. Ash tree leaves grow opposite each other on the branches and twigs. Ash leaves as a rule are pinnately compound. The leaves have a composition of an odd number of smaller leaflets, arranged opposite each other on a central axis known as a rachis. The odd leaf grows at the very end of the rachis.
The length of the rachis is of some value when trying to make correct ash leaf identification. Pumpkin ash and black ash possess two of the longest, with pumpkin ash sometimes as lengthy as 18 inches, and the black ash not far behind at 16 inches on its longest specimens. Medium-range length rachises of ash species belong to white ash and blue ash, with the central axis of their leaves developing to be between 8 and 12 inches. The Gregg ash and the velvet ash, both species from the southwestern portion of the United States, have smaller leaves, with the lengths in the 3- to 6-inch range for the latter and 1 1/2 to 3 inches for the former.
Numbers of Leaflets
The number of leaflets on one leaf will vary between the ashes, but because these leaflet numbers can fluctuate within a species, the task of easily identifying ashes in this manner gets problematic. For example, the Carolina ash of the southern Atlantic and Gulf Coast states can have from five to seven to sometimes nine leaflets, notes the "National Audubon Society Field Guide to Trees." The black ash can have from seven to 11 individual leaflets on each rachis. The lack of a fixed number of leaflets to look for contributes to making ash leaf identification difficult.
By meticulously measuring the lengths and widths of the leaflets on the ash leaves and then looking at their shapes, you can achieve some degree of confidence that you can identify them. One case is the leaflets on the pumpkin ash. Careful inspection reveals that they are between 3 and 7 inches long, from 2 to 3 inches in diameter, elliptical to oval in shape, and that they own smooth edges, with perhaps just the trace of teeth along their margins.
Color comes into consideration when trying to discern ash leaves, especially in the fall. The summer foliage of green ash is Kelly green, but in the fall, the foliage changes to yellow. Blue ash is a glossy darker shade of green, with the turn to yellow also occurring in autumn. While the leaves of white ash will typically become yellow in fall, a good number will change to tints of purple or burgundy, states the University of Connecticut Plant Database website.