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Trees with Compound Leaves

Hickories (Carya spp.)

A variety of hickories occur in the Arboretum forests. Identifying a tree as a hickory is relatively easy - it has alternate, compound leaves (several leaf blades associated with each axillary bud) with 5 to 9 leaflets. Identifying the species of hickory, however, is more challenging and often requires determining characteristics of the leaves, hickory fruits (outer husks and nuts), the terminal buds, and the bark. Furthermore, there is considerable variation of these characteristics within a species and hybridization of species produces individuals with intermediate or mixed characteristics. Three of the more common hickories found at the Arboretum are described below.

Mockernut Hickory (Carya tomentosa)

Mockernut Hickory Bark Mockernut Hickory Fruit Mockernut Hickory has leaves with 7 to 9 leaflets that are pubescent on the undersides. The globular to oval fruits are about 1 1/4 inches in diameter, with thick husks and a 4-ribbed nut. The tight bark has flat to rounded, interlaced ridges.

Pignut Hickory (Carya glabra)

Pignut Hickory Bark Pignut Hickory Fruit Pignut Hickory leaves typically have 5 to 7 glabrous leaflets (i.e. without hairs). The pear-shaped to ovoid fruits are about 1 inch in diameter, with thin husks and nuts that are not ribbed. The bark is relatively tight, has vertically oriented ridges that are rounded, and may be flaky.

Shagbark Hickory (Carya ovata)

Shagbark Hickory Bark A few Shagbark Hickories are found along our trails. Their leaves usually have 5 essentially glabrous leaflets. The 1 1/2 inch diameter fruit has a thick, rounded husk that splits all the way to the base, and a nut ridged on 4 sides. The distinctive bark is broken into long, shaggy plates.

Return to: Tree Identification Guide

Black Walnut (Juglans nigra)

Black Walnut Leaves Black Walnut Nuts Black Walnut Bark

Black Walnut, a relatively common tree at the Arboretum, is readily recognized by its large, pinnately compound leaves with 11-23 leaflets, its dark (almost black) ridged to platy bark, and its green (turning to yellow), ball-shaped fruits. It is considered a pioneer species invading fields and other open areas where it grows rapidly.

Black Walnut is an allelopathic plant, producing a chemical compound, hydrojuglone. When hydrojuglone is oxidized in air or soil, it becomes the toxic chemical juglone. This toxin (produced from the leaves, fruits, and roots) accumulates in the soil under the tree, inhibiting the growth of most other plants. A few plants, especially grasses, are unaffected by juglone and can grow under the tree canopy.

Black Walnut is a highly prized wood. Early settlers used it extensively for construction, but today it is primarily used for making furniture and gunstocks. The nuts are used in cooking, the oily husks have been used to make dyes and walnut stain, and the pulverized shells are used in oil drilling, cleaning jet engines, and for making activated charcoal.

The presence of black walnut trees at various sites around the Arboretum often indicates the location of former home sites. The fruits from these trees appear to be somewhat larger than normal, perhaps reflecting a selection by the homeowners of more vigorous cultivars.

Return to: Tree Identification Guide

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