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Ash Tree Identification (F1633)

Ash trees (in the genus Fraxinus) are susceptible to attack by the emerald ash borer (EAB), a non-native insect. The first step in determining if a tree has been infested with EAB is to make certain that it is an ash tree.

Joseph Zeleznik, NDSU Extension Forester


In North Dakota, green ash (Fraxinus pennsylvanica) is extremely common in native woodlands, shelterbelts and urban forests. Black ash (F. nigra) is native to a very small portion of northeastern North Dakota but sometimes is planted in urban areas as an ornamental.

White ash (F. americana) rarely is found in urban plantings and is not native. Mountain-ash and prickly-ash are not true ash species and are not susceptible to EAB.

Branch and Bud Arrangement

Branch arrangement

Bud arrangement

Buds and branches normally are found directly across from each other and not alternating along the stem. Note, however, that buds and branches may die; therefore, not every branch will have an opposite counterpart.

Leaves

Leaves

Leaves

Ash trees have compound leaves, composed of five to 11 leaflets. Leaflet margins are serrated and leaflets are opposite each other, except for the single leaflet at the tip. The only other tree species with opposite branching and compound leaves are boxelder (Acer negundo) and Amur corktree (Phellodendron amurense).

Bark

Bark

Bark young

On young trees, bark is relatively smooth and may have an orange cast. As trees age, the bark becomes gray and develops diamond-shaped ridges.

Seeds

Seeds

Seeds

Individual seeds are held in samaras that each have a single wing. Seeds occur in clusters that may stay on the tree well into winter.

Trees That Resemble Ash

Boxelder (Acer negundo)

Boxelder

Boxelder leaves

Boxelder has opposite branching and compound leaves, but the leaves have only three to five leaflets. In seed clusters, seeds always occur in pairs instead of singly. The twigs of boxelder trees often are blue/purple with a white, waxy covering.

Black walnut (Juglans nigra)

Black Walnut

Black Walnut

The compound leaves of black walnut contain nine to 15 leaflets, but the leaves occur in alternate placement on the branches. Fruits are large nuts contained in green husks that turn black in late fall.

Amur corktree (Phellodendron amurense)

Corktree

Corktree

This tree rarely is planted in North Dakota; it’s found only in a few landscapes. Like ash, corktree has compound leaves that are arranged opposite on the twigs. However, corktree leaves may contain as many as 13 leaflets. Leaflets are shiny and the fruit is distinctly different from ash.

Mountain-ash (Sorbus spp.)

European Mountain Ash berries

European Mountain Ash blossoms

European Mountain Ash leaves

Leaves of mountain-ash are compound, but the leaves have alternate placement on the branches. Mountain-ash flowers occur as creamy white clusters in early spring; fruits are red-orange berries.

March 2013
  

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