The Compound Nature of Ash Leaves
An ash leaf is characterized as “compound,” composed of multiple smaller leaflets. This contrasts with simple leaves, which are a single leaf blade attached directly to the stem. The arrangement of these leaflets is “pinnate,” where they are organized along a central stalk, much like the barbs of a feather.
A defining feature for identifying ash trees is the “opposite” arrangement of their leaves on the twig. This means that two leaves grow directly across from each other at each node along the branch. Most ash species exhibit this opposite arrangement, with their compound leaves consisting of a varying number of leaflets, commonly ranging from five to eleven. Often, there is an odd number of leaflets due to a single leaflet at the very tip of the central stalk.
Detailed Features of Ash Leaflets
These leaflets typically have an oval or elongated shape, often tapering to a pointed tip. While the exact shape can vary slightly among different ash species, this general form is consistent.
The edges, or margins, of ash leaflets can be either finely serrated, meaning they have small, saw-like teeth, or they can be smooth. Each leaflet generally connects to the central leaf stalk, known as the rachis, by a small stem called a petiolule, though this can be less pronounced on the terminal leaflet. The color of ash leaves is typically a dark green to blue-green during the growing season, transforming into shades of yellow or even reddish-purple in the autumn. Individual leaflets typically measure between 2 and 6 inches in length.
Differentiating Ash Leaves from Similar Trees
Distinguishing ash leaves from those of other trees can sometimes be challenging, especially since several species share some similar leaf attributes. Many trees have compound leaves, but few also have an opposite branch arrangement.
Box Elder (Acer negundo) is one tree that can be easily confused with ash, as it also features opposite, compound leaves. However, Box Elder leaves generally have fewer leaflets, typically three to five, and these leaflets are often more coarsely toothed or even lobed, unlike the more consistent shape of ash leaflets.
In contrast, trees like Hickory (Carya species) and Walnut (Juglans species) possess compound leaves, but their branches and leaves grow in an alternate pattern. Hickory leaves usually have five to seven leaflets, with the three at the end often being noticeably larger. Walnut leaves tend to be much longer, featuring a greater number of leaflets, commonly ranging from nine to twenty-three. Furthermore, Mountain Ash (Sorbus species), despite its name, is not a true ash and exhibits an alternate leaf arrangement along with producing berries, unlike the winged seeds of true ash trees.