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Juglans cinerea L. Butternut

Expanding leaves of a new shoot, with male catlins below

Also known as: white walnut.

Habitat

Butternut occurs in central, western, and southwestern New Brunswick, mostly on deep rich soils on lower slopes of valleys of the larger rivers. It grows scattered among other hardwoods, sometimes in small groups, but always with its crown exposed to light because it does not tolerate shade.

Medium-sized tree in the summer

Form

Butternut is a relatively short-lived tree (60 to 70 years) with a broad spreading, irregularly rounded crown. It commonly reaches heights of 13–20 m and stem diameters of 30–60 cm. The thick twigs and sparse, uneven branching at the crown’s periphery, help to distinguish this species in winter.

Crown of small-sized tree in winter

Morphology

The large leaves are deciduous and alternately arranged. They are 20–50 cm long, pinnately compound, with 11–17 finely toothed, broadly lanceolate to oval leaflets that have closely hairy undersides. The lateral leaflets are arranged more or less opposite to one another along a glandularly hairy rachis that extends from a relatively short petiole that has a broadened base.

Twigs, buds lateral buds often one above another at one leaf scar, shield-shaped leaf scars, and chambered pith exposed on older portion (bottom left)

The stout, strong, greenish-grey somewhat hairy new twigs carry large (12–18 mm long), closely downy terminal buds, and much smaller lateral buds (often two, one above the other) above each distinctive leaf scar. The leaf scars are large, broadly triangular, but with rounded edges. They have three groups of vein scars, and a distinct hairy band, or lip, along the upper margin. The pith of a new twig is cinnamon brown and, as it ages (as in a 2-year-old twig), it becomes chambered (so, if cut lengthwise, it appears ladder like).

An expanded male catlin

The male flowers are produced in thick, green catkins 6–14 cm long, that arch out and down from lateral buds below the shoots and leaves beginning to grow out from the terminal buds above. The female flowers are much less conspicuous, occurring in small groups on short stems arising in axils of new leaves some distance along the stronger of the new shoots. The distinctive fruits develop from the female flowers as the season progresses. By early fall they are 4–6 cm long, ovoid, green, stickily hairy structures. Inside the husk is the nut with its hard, thick, woody, convoluted shell and, inside the shell, the seed—which is the edible “nut.” Handling the fruits turns skin yellow.

Bark of stem, 18 cm in diameter

The bark is smooth and light brownish grey when young; it becomes deeply and openly furrowed with intersecting flat-topped ridges when older, but remains brownish grey.

Notes

Butternut wood is semi ring porous, pale reddish brown, fairly soft and weak, but valued for veneer, furniture, cabinet work, and interior trim. However, it is seldom available because large trees are scarce. The nuts are an interesting food source, but the primary beneficiaries are squirrels. A useful yellow dye can be extracted from the fruit husks.

Butternut is increasingly threatened by butternut canker, a fatal disease caused by a fungus, Sirococcus clavigignenti-juglandacearum. This fungus induces multiple cankers at the base of the trunk and branches, which coalesce and girdle the tree, resulting in partial to complete death. To date, no control for this disease exists.

Female flowers clustered along a stem in the axil of a new leaf

Developing fruit in late summer