Horse Chestnut family (Hippocastanaceae)
This deciduous tree is 40-100' tall, forming an erect trunk about 1-5'
across and a large crown of branches and leaves. Depending on its
maturity and location, the crown of this tree is ovoid to broadly
oblongoid in outline. Upper to middle branches are ascending, while
lower branches are slightly drooping or widely spreading; twigs have a
tendency to curve upward toward their tips. Trunk bark of mature trees
is gray, somewhat fissured, and scaly, although not particularly thick.
The bark of branches are gray and more smooth, while twigs are light
brown and smooth with scattered white lenticels (air pores). Young
shoots are light green, terete, and mostly glabrous. Pairs of opposite
leaves occur along the twigs and young shoots. These leaves are
palmately compound with 5-9 sessile leaflets (typically there are 7
leaflets per leaf). Individual leaflets are 3-8" long and 1-3" across;
they are oblanceolate in shape, while their margins are mostly
serrated, although they become toothless toward their bases
and doubly serrated toward their tips. The tips of leaflets
taper abruptly into short narrow tips (acuminate), while their bases
are narrowly wedge-shaped (cuneate). The outer lateral leaflets and
terminal leaflet are larger in size than the inner lateral leaflets.
The leaflets are widely spreading or droop
slightly from their bases.
The upper leaf surface is yellowish
green during the spring, becoming dark green during the summer; it
is glabrous. The lower leaf surface is more pale than the upper
surface, and usually glabrous, although it sometimes has brownish
strips of fuzzy hairs along the central veins of the leaflets.
The petioles of the compound leaves are 3-10" long, light green,
terete, and glabrous. Panicles of flowers about 6-12" long and 3-6"
across occur at the tips of twigs. These panicles are more or less
erect and a little wider at their bases than their apices. There are
typically 25-50 flowers per panicle. The flowers along the upper
half of the panicle are male (staminate), while the flowers along the
lower half of the panicle are both male and female (perfect). Each
flower is about 1" long and 1" across, consisting of a
short-tubular calyx with 5 teeth, 5 spreading white petals, 5-8
strongly exserted stamens, and a pistil with a strongly exserted style.
The calyx is light green or yellowish green. The similar-sized petals
are oval in shape, rather wrinkly, finely pubescent, and ciliate
along their margins. The two upper petals have conspicuous patches of
yellow toward their bases that become red as the flowers age. The
stamens have white filaments and orange-brown anthers, while the style
is white. Both the filaments and style are finely pubescent toward
their bases. The central rachis, lateral stalks, and pedicels of
each panicle are light green to yellowish green, terete, and sparsely
canescent; the pedicels of the flowers are relatively short (usually 1"
or less in length).
The blooming period occurs during late spring,
lasting about 2-3 weeks. The flowers have a sweet honey-like fragrance.
Afterwards, perfect flowers are sometimes replaced by seed capsules
(usually only 1-3 seed capsules are produced per panicle of flowers).
These seed capsules are about 2" across and ovoid-globoid or globoid in
shape. The leathery outer husks of these seed capsules are initially
light green, becoming brown with age; they are more or less covered in
prickles. Each husk contains 1-2 seeds (rarely 3 seeds). These nut-like
seeds are ¾–1½" across and globoid or subgloboid in shape; they are
dark brown and smooth, except for 'eyes.' The latter are tan and
slightly rough-textured. At maturity, these seed capsules fall to the
ground and their husks divide into 3 segments, releasing the seeds. The
woody root system produces a deep taproot and more shallow lateral
roots. This tree reproduces by reseeding itself.
The preference is full or partial sun, moist to dry-mesic
conditions, and soil containing clay-loam, silt-loam, or loam.
Because the large seeds lose their viability quickly, they should be
planted in the ground or in a deep pot shortly after they are produced
during the autumn. This trees develops fairly quickly, and it is able
to produce flowers and seeds after about 20 years. Longevity of healthy
trees is typically about 100 years. Winter hardiness is excellent (to
Zone 3). Sometimes the leaves are affected by disease organisms, but
this is rarely a severe problem.
Range & Habitat:
non-native Horse Chestnut is uncommon in Illinois (see Distribution
Map). Although it is occasionally cultivated as a landscape
parks and yards, this tree does not escape from cultivation very often.
Horse Chestnut is native to SE Europe. Habitats of escaped trees
include disturbed open woodlands, roadsides, edges of yards, parkland,
vacant lots, and waste areas. Areas with a history of disturbance are
preferred. So far, this tree has not become invasive in Illinois. In
the United States, isolated naturalized populations occur primarily in
the Northeast and Midwest.
Associations: Robertson (1929) observed the
bumblebees, and other long-tongued bees (Anthophora,
visiting the flowers for nectar. Some insects feed destructively on
Horse Chestnut. For example, two highly polyphagous
insects, adults of the Japanese Beetle (Popillia
larvae of the White-marked Tussock Moth (Orgyia leucostigma),
the leaves of this tree, while the larvae of the Maple Twig Borer Moth
(Proteoteras aesculana) bore into its young shoots
(Cranshaw, 2004; Miller, 1987). Several armored scale insects are
sometimes found on the bark, including the San Jose Scale (Diaspidiotus
perniciosus), False San Jose Scale (Diaspidiotus
Oystershell Scale (Lepidosaphes ulmi), and White
(Pseudaulacaspis pentagona). All of these scale
insects are polyphagous
(ScaleNet, 2014). The foliage, bark, and seeds of the Horse Chestnut
are toxic because they contain saponins and a coumarin glycoside,
Aesculin. As a result, they are rarely consumed by mammalian herbivores.
A yard in Urbana, Illinois.
This tree can become quite large in size. It has attractive and
fragrant flowers. In Illinois, Horse Chestnut
(Aesculus hippocastanum) can be distinguished from
native Aesculus spp.
(Buckeyes) by the shape of its leaflets: they are widest toward their
tips (oblanceolate in shape), whereas the leaflets of native species
are widest toward the middle (elliptic in shape). Horse
Chestnut has been hybridized with the native Red Buckeye (Aesculus
This hybrid resembles the Horse Chestnut, but its flowers are
predominately pink, rather than white. Buckeye trees and the Horse
Chestnut have been reassigned to the Soapberry family (Sapindaceae)
recently as a result of genetic analysis. The wood of Horse Chestnut is
light-colored, fine-grained, and soft. It is rarely used for commercial
purposes. In spite of its common name, this tree is not closely related
to chestnut trees (Castanea spp.).