Description: This tree is 80-120' tall at maturity, forming an ovoid crown and tall trunk. On mature trees, the trunk is 3-6' across, developing a deeply furrowed bark that is gray to nearly black. The bark of branches is more smooth and gray. Alternate compound leaves are 1-2' long and ½' across; their structure is odd-pinnate, although the terminal leaflet is often deformed or missing. Individual leaflets are about 3" long and 1" across; they are lanceolate or ovate-lanceolate, serrated along their margins, and nearly sessile. The upper leaflet surface is medium green and glabrous, while the lower surface is pale green and short-pubescent along the ribs of the veins. The rachis (central stalk) of each compound leaf is light green to pale brown and short-pubescent. The rather stout petioles of the compound leaves are 3-6" long, light green to greenish brown, and pubescent.
Black Walnut is
monoecious with individual trees bearing both male (staminate) and
female (pistillate) florets. The male florets occur on dangling
cylindrical catkins about 3-6" long. Individual male florets are about
1/8" (3 mm.) across, consisting of a short tubular calyx with 2-6 lobes
and
15-40 stamens. The female florets occur on short spikes in groups of
2-5. Individual female florets are about 1/8" (3 mm.) across,
consisting of a
short tubular calyx with 4 lobes and a pistil with a pair of styles.
The calyxes of both male and female florets are short-pubescent. The
blooming period occurs during late spring as the leaves begin to
develop. The florets are cross-pollinated by the wind, although female
florets are often self-fertile should cross-pollination fail to occur.
Fertile female florets develop into ovoid-globoid nuts about 2½" long
and 2" across that occur either individually or in pairs. These nuts
are covered with thick green husks that later become yellowish brown
and finally black. The husks are covered with a pimply surface and they
are aromatic. When the nuts are harvested before their husks blacken,
the shells of the nuts are light brown and wrinkled. Each nut is
incompletely 4-celled and contains edible meat that is sweet and
slightly bitter. The root system consists of a deep taproot and widely
spreading lateral roots. This tree reproduces by reseeding itself. The
deciduous leaves turn yellow and fall to the ground rather early during
the autumn.
Cultivation:
The preference is full or partial sun, moist conditions, and deep soil
containing loam, silty loam, or sandy loam. The pH of the soil should
be slightly acid to neutral. This tree tolerates spring flooding if it
is temporary. Because of the deep taproot, it is difficult to
transplant successfully. To germinate the nuts, they must be subjected
to cold winter temperatures for 90-120 days. The resulting seedlings
may produce nuts as early as 5 years, but significant production of
nuts doesn't occur until they become 10-15 years old.
Range & Habitat:
In Illinois, the native Black Walnut is a common tree that is probably
found in
every county of the state (see Distribution
Map). Habitats consist of rich mesic woodlands, moist
bottomland woodlands in valleys and along rivers, and the bases or
lower slopes of bluffs. Black Walnut is found in deciduous woodlands
with moisture-loving maple, hickory, oak, and ash trees. Sometimes this
tree is planted deliberately because of its edible nuts and valuable
wood.
Faunal Associations:
Miscellaneous insects use Black Walnut as a food source, particularly
the caterpillars of many moths (see Moth Table). Other insect feeders
include the wood-boring larvae of long-horned beetles, leaf beetles,
stink bugs, plant bugs, aphids, and species from other families (see Insect
Table). The nuts are an important food source for the Gray
Squirrel, Fox Squirrel, Red Squirrel, and Eastern Chipmunk; these
animals bury the nuts in secret caches and help to distribute them to
new locations. White-Footed Mice also feed on the nuts, while rabbits
sometimes gnaw on the stems of young trees during the winter.
Photographic Location:
Meadowbrook Park in Urbana, Illinois.
Comments: Because of its nuts and high quality wood, Black Walnut is a valuable tree, although a rather messy one. The rotting husks of the nuts can stain side sidewalks and driveways a brown-black color that is difficult to remove. Even immature green husks can stain your fingers yellow when they are handled. The closest relative of Black Walnut in Illinois is the less common Juglans cinerea (Butternut), which has been declining in numbers because of disease. The nut husks of Butternut are more smooth and pubescent than those of Black Walnut, and its nuts are a little smaller in size and more narrowly ovoid in shape. The young branchlets of Butternut are downy, while those of Black Walnut are smooth. In general, both Butternut and Black Walnut differ from the related Carya spp. (Hickories) by their unsegmented nut husks and the chambered (or partitioned) pith of their twigs.