Green ash (Fraxinus pennsylvanica) is a member of the olive family, and the species of ash tree with the largest geographic range in the United States. Green ash grows across almost the entire Eastern part of the nation and as far west as the Rocky Mountains. Green ash may prove difficult to tell apart from the other types of ash trees that grow in the U.S. The key to identification of green ash is to pay the utmost attention to even the smallest details of the tree.
Look for a tree that grows to a mature height of between 60 and 70 feet, with a spread of about 45 feet across in its upper canopy. Green ash is a medium-sized species and has an oval crown of branches. The trunk can be as wide as a foot and a half and the leaves fall from the tree every autumn.
Observe the foliage of a green ash, looking for a leaf that botanists term as being pinnately compound. Pinnate means that the separate leaflets that comprise the compound leaf grow in two rows on a central axis, called a rachis. Green ash has from seven to nine individual leaflets that grow on a rachis and compose one single leaf. The leaflets are as long as 5 inches, shaped like the sharp head of a spear, and a shiny shade of green. The entire compound leaf may be as long as a foot, says the University of Connecticut Plant Database website.
Watch for the leaves of green ash to change to yellow in the autumn. This trait adds to the appeal that makes the tree a very attractive ornamental species and one that often adorns lawns, streets and campuses.
Examine the flowers on a green ash. The species has male and female flowers that grow on separate trees. The flowers have no petals, are a light green or purple color and emerge after the leaves do in the spring. The female flowers develop in long clusters, according to the Virginia Department of Forestry website, while the male flowers grow in tighter groupings.
Study the samaras into which the flowers on the female trees turn. The samaras are a seedpod that contains the green ash tree's seeds. The "National Audubon Field Guide to Trees" states that these samaras resemble keys, hanging in cluster from the female trees as they change from a green color to a tan hue. Once mature, the 1.5- to 2.5-inch-long samaras fall off the tree and create quite a mess. This makes the male tree the preference of many landscapers, as the males will not litter your property.
Inspect the other features of the green ash tree that may help you to recognize this species. The new twigs are green but turn gray over time. The bark is grayish to brownish in color, with furrows and ridges on older specimens. Green ash has dark red-brown buds in the winter that open into the leaves in spring. Green ash usually grows where the soil is fertile and moist. The tree prefers full sun and you will often discover them near the banks of streams.