Identifying characteristics:
The black walnut is a deciduous tree growing to 90 feet with a broad, rounded,
rather open crown and a very straight trunk 2 to 3 ft in diameter. The leaves are 1 to 1.5 ft long with 11
to 23 alternate, finely-toothed, short-stalked, yellow-green leaflets which
are smooth above and faintly hairy beneath. The terminal leaflet is often
suppressed so that the leaf ends in 2 leaflets. Male flowers
are borne in catkins and female flowers in clusters. The walnut fruit is a round nut in a hard, corrugated
shell. The shell is surounded by a thick, slightly hairy, semi-fleshy husk
which is yellow-green, turning black and once used by poineers to make dye.
The terminal bud is ovoid, blunt and slightly hairy. Lateral buds
are smaller and often suppressed. Leaf scars are curved at the top and not
fringed on top with a "fur collar" as is the butternut (J.
cinerea). Black walnut bark is
dark gray or black and furrowed with deep, interconnecting ridges that become
blocky.
Similar species:
- butternut (Juglans cinerea)
Ecology:
Distribution: Native to Iowa, this tree has a range from Massachusetts
to Minnesota, south to northern Florida and Texas, preferring the fertile,
moist, well-drained soils of bottomlands and lower slopes.
Habitat: The root system is deep, wide-spreading, usually with a tap root. A toxic substance, juglone, is leached from the roots and fallen leaves, inhibiting the growth of many plants, including young walnut seedlings. Diseases which affect walnuts include a walnut anthracnose fungus (which causes severe defoiliation and canker of stems), wilt, blight and witches' broom. Aphid, walnut caterpillar and walnut scale are the known insect pests of walnut trees.
Uses:
Wood: The wood is heavy, hard, strong, easily worked and has
an attractive grain. Iowa is a leading producer of walnut timber which is
the single most important tree in terms of price per tree. Noted as the
finest lumber in North America, this wood was shipped to England from Virginia
as early as 1610. Products include gunstocks, veneer and fine furniture.
Wildlife: The nuts make up 10% of squirrels' diet and they help to disperse the seeds. Red-bellied woodpeckers and beavers also eat the nuts, and the strongly flavored, oily kernel makes it commercially important for baking and flavoring.
Horticulture: Walnut trees are rarely planted as lawn trees-they require exacting soil conditions, are subject to wind and ice damage, produce messy fruit and the toxic substance from their leaves may kill some ornamentals in the vicinity.
