Description:
This tree is 50-100' tall at maturity, forming a single trunk about
2-3½' across and an open plume-like crown that is somewhat flattened at
its apex. Trunk bark of mature trees is light gray to gray-black and
divided into large
flat plates with upturned margins; these plates are slightly scaly and
they are separated by shallow furrows. The bark of branches and twigs
is more smooth, brown, and hairless, while young shoots are light green
and pubescent. Alternate compound leaves occur along the twigs and
young shoots. These leaves are evenly pinnate or bipinnate and 6-14"
long. Pinnate leaves have 5-11 pairs of simple leaflets, while
bipinnate leaves have 4-7 pairs of pinnate leaves that are each divided
into 5-11 pairs of simple leaflets. There are no terminal leaflets.
The rachis of each compound leaf is light green and pubescent.
The leaflets are ¾-1½" long and about 1/3 as much across; they are
oblong to lanceolate-oblong and slightly crenate along their margins.
The upper surface of the leaflets is yellowish green to dark green and
hairless, while the lower surface is more pale and either hairless or
minutely hairy. The leaflets have very short petiolules (basal
stalklets) that are less than 1/8" (3 mm.) long. Along the trunk, there
are
usually both simple and branched thorns up to 8" long; there are also
simple and tripartite thorns along the lower branches. However, there
is also a thornless variety (var.
inermis)
of Honey Locust that is
uncommon in the wild, although often cultivated.
The small greenish
yellow flowers are produced in racemes about 2-5" long; they are
usually male (staminate) or female (pistillate), although sometimes
perfect (both staminate & pistillate). Individual male flowers
have
a calyx with 5 lobes, 4-5 petals, and 3-10 stamens, while individual
female flowers have a calyx with 5 lobes and a pistil with a single
style. Individual perfect flowers have both a pistil and several
stamens. The blooming period occurs from late spring to early summer
for about 2 weeks. The flowers have a sweet fragrance. Fertile female
flowers are replaced by flattened seedpods that become 6-14" long and
1-1½" across at maturity. Mature seedpods are dark brown, hairless, and
often hooked or spirally twisted. Each seedpod contains several large
seeds that
are reniform in shape and about 1/3" (8 mm.) long; they have hard seed
coats.
The seeds are embedded in a thick sweet pulp. The seedpods fall to the
ground unopened during the late fall or winter. The woody root system
has a taproot and abundant lateral roots that are widely spreading and
deep. The deciduous leaflets turn yellow during the autumn.
Cultivation:
This adaptable tree prefers full to partial sunlight and moist to
dry-mesic conditions. It will flourish in almost any type of soil
(pH range 6.0-8.0) if it is not too acidic. Both temporary flooding and
hot dry weather are tolerated. The root system doesn't fix nitrogen in
the soil. New trees can be propagated by seeds or vegetatively by
cuttings. Growth and development is fairly fast; young trees can
produce seedpods in as little as 10 years. Longevity of healthy trees
is typically 100-150 years. One of the advantages of Honey Locust as a
landscape tree is the light shade that is cast by its open crown; this
allows the survival of turfgrass and other plants.
Range
&
Habitat: The native Honey Locust has been found in almost
every county
of Illinois; it is common. Habitats include
upland woodlands, bottomland woodlands, woodland openings, woodland
borders, powerline
clearances in wooded areas, savannas, edges of
limestone glades, thickets, fence rows, pastures, and roadsides. This
tree colonizes disturbed areas that are relatively open; it is
intolerant of shade. Because of the thin bark, Honey Locust is
vulnerable to wildfires. The thornless variety of this tree is often
cultivated as a landscape plant; it often escapes in both urban and
suburban areas.
Faunal
Associations: The flowers are
cross-pollinated primarily by small bees and flies. Both nectar and
pollen are available as floral rewards to such visitors. The
caterpillars of
Epargyreus
clarus (Silver-Spotted Skipper) feed on
the foliage of Honey Locust. Several moth caterpillars prefer this tree
as a host plant:
Catocala illecta (Magdalen Underwing),
Catocala
innubens (The Betrothed),
Catocala minuta
(Little Underwing),
Spiloloma
lunilinea (Moon-Lined Moth),
Sphingicampa bicolor
(Honey Locust Moth),
and
Sphingicampa bisecta
(Bisected Honey Locust Moth). Several
leafhopper species also prefer this tree as a host plant:
Erythridula
aenea,
Erythridula
brundusa,
Erythridula
clavata,
Erythridula
diffusa,
Erythridula
gleditsia, and
Macropsis
fumipennis
(Honey
Locust Leafhopper). Other insect feeders include the treehopper
Micrutalis clava,
Diaphnocoris chlorionis
(Honey Locust Plant Bug) and
other plant bugs,
Anomoea
flavokansiensis and other leaf beetles, the
larvae of
Agrilus
difficilis (Honey Locust Borer) and other wood-boring
beetles, the larvae
of the seed weevil
Amblycerus
robiniae, and the larvae of
Dasineura
gleditchiae (Honey Locust Pod-Gall Midge). See the
Insect
Table for a
more complete listing of the invertebrate species that feed on this
tree. Some mammals and birds also use Honey Locust as a source of food.
The seedpods with their edible sweet pulp are eaten by cattle, sheep,
goats, deer, opossums, tree squirrels, crows, starlings, and Bobwhite
quail. It is thought that some extinct megafauna of the ice age,
including the American Mastodon, also ate these seedpods and helped to
distribute the seeds into new areas. Cattle, deer, rabbits, and
groundhogs browse on the foliage of seedlings, saplings, or the
lower limbs of trees; rabbits also gnaw on the bark of young trees
during the winter.
Photographic
Location: Busey Woods and other locations in
Urbana, Illinois.
Comments:
Wild trees are often formidably armed by thorns; it is possible that
this functioned as a defense against the American Mastodon and other
large megafauna of the last ice age. Today, these thorns discourage
squirrels, opossums, raccoons, and humans from climbing this tree. The
only other tree that Honey Locust can be confused with in the Midwest
is Black Locust
(
Robinia pseudoacacia).
Black Locust has slightly larger leaflets,
fewer thorns, shorter seedpods, and more showy white flowers. These
flowers have a pea-like floral structure that is typical of species in
the Bean family (Fabaceae). The greenish yellow flowers of Honey
Locust, in contrast, have a more conventional floral structure.