Identifying characteristics:
The black locust is a fast-growing, deciduous tree to 50 feet with a straight
trunk and an open, irregular crown. The leaves
are once-pinnately compound and alternate, with 7 to 21 leaflets each 1.5
to 2 inches long. The leaflets are elliptic, with entire margins and a dark,
bluish-green color, turning yellow-green and dropping early in the fall.
The flowers are produced May to
early June in dense racemes 4 to 8 inches long. The extremely fragrant flowers
are 1 inch wide and creamy-white with a yellow blotch on the uppermost petals,
remaining showy for 7 to 10 days. The fruit
is a flattened, brown-black pod, tapering abruptly or rounded at the ends,
containing 3 to 8 dark, spotted seeds. Pods may remain on the tree some
time after maturing in October. The twigs are characteristically zig-zagged,
with pairs of spines up to a half inch long at the nodes. The buds
are apparently absent as they are embedded in the leaf scars. The terminal
bud is absent. The reddish-brown bark
is deeply furrowed into thick, interlacing, fibrous ridges.
Similar species:
Ecology:
Distribution: Native to the central Appalachian and Ozark mountains
and southern Illinois, this tree now reproduces on its own throughout eastern
North America and parts of the West. Naturalized or escaped from cultivation,
it grows throughout most of Iowa along the edges of woods and in waste areas
as thickets or groves.
Habitat: The black locust is extremely adaptable to a variety
of soils and climates, although it prefers rich, moist, loamy soils of limestone
origin. Because it fixes nitrogen in root nodules, this species can grow
on sterile, sandy soils, helping to improve the condition of the soil. Tolerant
of dry and saline conditions, the black locust has a wide-spreading root
system and is often used for reclamation plantings of strip-mined or eroded
land. The locust borer is the most damaging insect pest, generally killing
trees before they reach mature size. The US Forest Service has worked to
develop borer-resistant clones. Other pests and diseases of the black locust
include canker, leaf spot, powdery mildew, locust leaf miner and scale.
Uses:
Wood: The wood is more resistant to decay and possesses a higher
fuel value than any other broad-leafed tree native to temperate North America.
The wood is hard, strong, heavy and shrinks and swells less than that of
most other trees. It is used for fence posts, railroad ties, mine timbers,
tree nails, insulator pins and fuel. The wood is widely sought for ship
building and was exported to England in the last century for this purpose.
Wildlife: Bees make delicious honey from the nectar, and quail and squirrels eat the seeds. Black locust thickets are useful nesting sites for birds and form protective cover for wildlife.
Horticulture: This tree has long been used as an ornamental in Europe, but is seldom used in the US-perhaps because it provides poor shade and is attacked by many insect pests. It is a good tree for use in difficult conditions such as highway cutouts and strip-mined areas. Several cultivars have been developed: 'Aurea', with young growth emerging yellow; 'Purple Robe', with pink flowers and bronze new leaves; 'Pyramidalis', a columnar, spineless cultivar.
