This perennial wildflower develops a rosette of basal leaves, from
which there develops one or more flowering stalks about 1¾-4' tall. The
blades of the basal leaves are ½-2' long and 1½-6" across; they are
broadly oblong-elliptic in shape and finely crenate-serrate along their
margins. The petioles of the basal leaves are often as long as the
blades. The basal leaves are widely spreading and rather floppy; their
margins often undulate up-and-down. The stems of Horseradish are light
to medium green and glabrous. Alternate leaves become smaller in size
as they ascend these stems; their blades are 1-6" long and ¼-2" across.
The blades of alternate leaves are narrowly elliptic to broadly
oblong-lanceolate in shape and their margins are coarsely
crenate-serrate to shallowly pinnatifid; they are sessile or with short petioles. The upper blade surfaces of
both basal and alternate leaves are medium to dark green and glabrous,
while their lower surfaces are a more pale shade of green and glabrous
The central stem and upper axillary stems terminate in either racemes
of flowers about 4-16" in length. The flowers bloom toward the apex of
each raceme (or branch of a panicle), while seedpods develop below.
Each flower spans about 1/3"
(8 mm.) across, consisting of 4 white petals, 4 light green sepals, 6
stamens, and a pistil with a short style. The petals are about twice
the length of the sepals. The ascending pedicels are ¼-¾" in length,
light green, and glabrous, becoming longer as the seedpods develop. The
central stalks and branches of the racemes and panicles are light green
and glabrous. The blooming
period can occur from mid-spring to mid-summer and lasts about 2
months. The flowers are replaced by cylindrical seedpods up to ¼" (6
mm.) long; each seedpod can contain up to 8 seeds. The root system
consists of a stout taproot and stout rhizomes. Clonal colonies of
plants are often produced.
The preference is full
or partial sun, moist conditions, and fertile soil containing loam or
silt-loam. Because of its underground rhizomes, Horseradish can spread
The non-native Horseradish is
occasional in most areas of Illinois, except in the SE section of the
state, where it is rare or absent (see Distribution Map
was introduced into North America from Europe during colonial times; it
is native to SE Europe and parts of SW Asia. Habitats include
streambanks, ditches, fence rows, low areas along roads and railroads,
abandoned fields, vacant lots, disturbed open woodlands, and waste
areas. Horseradish is still cultivated in gardens as a culinary herb.
It is usually found in disturbed areas.
The nectar and pollen of the flowers attract
flies, small butterflies, and probably other insects. Several leaf
beetles (Chrysomelidae) have been observed to feed on Horseradish,
(Horseradish Flea Beetle), Phyllotreta bipustulata
(see Clark et al., 2004). These species are
beetles (a subfamily of leaf beetles) that feed on the foliage. Other
insect feeders include Murgantia
(Harlequin Bug), the
caterpillars of Lascoria
(Ambiguous Moth), and the
caterpillars of Pieris
(Cabbage White). Because of high levels of
mustard oil from the conversion of glucosinolates, Horseradish can
produce toxic effects on mammalian herbivores, especially the pungent
A roadside ditch in NW Ohio, and the Toledo
Botanical Garden in Toledo, Ohio.
In the United States, the thick roots of Horseradish are grated to
flavor various sauces for food (primarily dishes of beef,
pork, and seafood). Such sauces usually contain vinegar, mayonnaise, or
pureed tomatoes. Because of the warm climate during summer and the
long growing-season, Horseradish usually produces both seedpods and
viable seeds in Illinois and other areas of the lower Midwest.
Apparently this rarely happens in Great Britain and other areas of
Europe where the climate is cool and the growing-season is too short.
However, Horseradish is readily propagated by dividing its roots.
Because of the size and abundance of its flowers, Horseradish is fairly
showy while it is in bloom, especially for a species in the Mustard
family. It is also larger in size than most species in this plant
family. Horseradish can be distinguished from similar species by the
size of its white flowers (about 1/3" across), the appearance of its
basal and alternate leaves, its small cylindrical seedpods, and the
pungent odor of its roots. Because the classification of Horseradish
has been unstable in the past, it is sometimes referred to as Armoracia
, and Rorippa