Ash trees, belonging to the genus Fraxinus, are deciduous trees common across North America and Europe. Learning to recognize the specific features of these trees is important for assessing their health, especially due to threats like the Emerald Ash Borer (EAB). Focusing on key characteristics like branching pattern, leaf structure, bark texture, and seasonal seeds provides a reliable method for identification.
Opposite Branching Pattern
The most distinguishing trait of an ash tree, observable year-round, is its opposite branching pattern. This means that lateral branches and buds grow directly across from one another on the stem, rather than in a staggered, or alternate, arrangement. This symmetrical growth habit is relatively uncommon in forest trees, making it a reliable first check for identification.
When checking for this pattern, look higher up the branches and at several points, as a broken branch can sometimes create a false alternate appearance. The terminal bud, located at the tip of the twig, is paired with a lateral bud immediately below it. A helpful mnemonic device for remembering the few trees that exhibit this pattern is “MAD-Buck,” which stands for Maple, Ash, Dogwood, and Buckeye.
Compound Leaf Structure
Ash trees possess compound leaves, which is the second major identifier used to distinguish them from other opposite-branching species. A compound leaf is one where multiple smaller leaf blades, called leaflets, are attached to a single central stalk, or rachis. This structure differs from a simple leaf, which consists of only one blade attached to the twig.
Ash leaves are specifically pinnately compound, meaning the leaflets are arranged in pairs along the central stalk. Most ash species typically have between five and eleven leaflets per leaf, with a single leaflet positioned at the tip. The only other common opposite-branching tree with compound leaves is the Boxelder, which usually has only three to five leaflets.
Bark Texture and Tree Shape
The texture of the bark is a useful feature for identifying mature ash trees, especially during the winter when leaves are absent. Mature White and Green Ash trees develop a distinctive, deeply furrowed bark. These prominent ridges often interlace, creating a recognizable diamond or kite-shaped pattern over the trunk.
Young ash trees have bark that is comparatively smooth and gray, requiring the use of branching and leaf characteristics for identification. Regarding overall form, the ash tree generally maintains an upright, oval to rounded silhouette when young, with a relatively dense canopy. As they age, the shape often becomes more irregular, growing to heights between 50 and 80 feet.
Seasonal Identification: Ash Seeds
Ash trees produce a specific type of fruit known as a samara, which is a key seasonal identifier, usually present from late summer through winter. The samara is a dry, single-winged fruit that aids in wind dispersal. Ash samaras are often described as paddle-shaped or oar-shaped, with the seed located at one end and the wing extending outward.
These winged seeds hang in dense clusters from the branches, often persisting on the tree after the leaves have fallen. The color of the samaras changes as they mature, moving from green to pale green, then yellow-green, and eventually to a tan or dark brown.