Juglans nigra (Black Walnut)
|Also known as:
|part shade, sun; average moisture; hardwood and mixed forest, savannas, banks
|May - June
|to 130 feet
|Wetland Indicator Status:
|GP: FACU MW: FACU NCNE: FACU
|MN county distribution (click map to enlarge):
|National distribution (click map to enlarge):
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Male and female flowers are borne separately on the same branch (monoecious). Male flowers are in clusters called catkins, 2 to 4 inches long, pendulous in flower, single in the leaf axils of 1 year old branchlets, the flowers yellowish to green with up to 50 stamens per flower.
Female flowers are in a short spike at the tip of this year's new branchlets with 1 to 4 flowers in the spike, the flowers with a stout, green ovary covered in sticky hairs and a pair of broad, spreading, red-tinged stigma at the top.
Leaves and stems:
Leaves are alternate, usually crowded at branch tips and appearing whorled, 8 to 24 inches long, compound with 12 to 19 leaflets. Leaflets are lance-oblong, 2¼ to 6 inches long, ½ to 2 inches wide, finely toothed around the edges, with an abrupt taper to a pointed tip, asymmetrical and rounded to straight across at base, and very short-stalked. The terminal leaflet is rather smaller than the lateral leaflets and often absent altogether. The upper surface is dark green and sparsely hairy, the lower is paler in color and covered in a mix of glandular and non-glandular hairs. The compound leaf stalk is green and covered in sticky hairs.
Buds are light brown and covered in short fuzz, the terminal bud round to oval and slightly flattened. New twigs are green to olive-brown, variously covered in a mix of glandular and non-glandular hairs, becoming smooth the second year. Leaf scars are more or less Y or heart-shaped with a notch at the tip. Branch pith is chambered and light brown.
Fruit is usually spherical, 1½ to 3 inches in diameter, about as long as wide, the outer husk greenish and not sticky. Inside is a sweet nut with a hard shell. Fruits are usually single or in pairs at branch tips.
Black Walnut is a common forest species in the eastern half of North America and reaches the northern edge of its range in Minnesota. It is prized both for its wood, used for furniture and veneers, as well as the tasty nuts. The natural range extends to Twin Cities area, but it's also been planted much farther north and can be seen in landscapes and parks into the Arrowhead region. In recent years it has fallen prey to Thousand Cankers, a fungal disease primarily spread by the walnut twig beetle, which has spread throughout the western US with a second infection from the mid-Atlantic states into Indiana. The disease is not known to be in Minnesota or surrounding states at this time, but it is heading our way. Black Walnut closely resembles the related Butternut (Juglans cinerea), which is distinguished by more elongated, sticky, oval-elliptic fruits that are usually clustered 3 to 5, dark brown pith in the twigs, the leaflet hairs are branched, the terminal leaflet is about the same size as lateral leaflets, and leaf scars are flatish to convex at the tip and have a band of velvety hairs along the top edge. Black Walnut fruits can also stain your hands black, and broken twigs and crushed leaves give off a strong, pungent odor. Butternut does neither of these.
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- Black Walnut tree
- Black Walnut tree
- fall color
- leaves appear whorled at branch tips
- glandular hairs on leaf stalks
- comparison of Juglans cinerea and Juglans nigra leaf scars
- comparison of Juglans cinerea and Juglans nigra pith
Photos by K. Chayka taken in Ramsey County. Photos courtesy Peter M. Dziuk taken at various locations in the Twin Cities metro area. Other photos courtesy Heather Holm.
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