garlic mustard | skymeadows

garlic mustard (Alliaria petiolata)

COMMON NAMES:
garlic mustard plant
garlic root
garlicwort
hedge garlic
Jack-by-the-hedge
Jack-in-the-bush
mustard root
poor man's mustard
sauce-alone
garlic mustard

SCIENTIFIC SYNONYMS:
Alliaria alliaria (L.) Britton
Alliaria officinalis Andrz. ex M. Bieb.
Erysimum alliaria L.
Sisymbrium alliaria (L.) Scop.

CONFIRMATION STATUS: Pending confirmation.

TAXONOMY: The currently accepted scientific name of garlic mustard
is Alliaria petiolata (M. Bieb.) Cavara & Grande. The Cardamine spp.
(bitter cresses) are somewhat similar in appearance to garlic mustard,
but they have larger flowers on longer pedicels, and their leaves are never
coarsely toothed. Some members of the Mint Family have leaves that
resemble those of garlic mustard, but the Mints always have opposite
leaves and their stems are conspicuously 4-angled.

NATIVE STATUS: Introduced, United States and Canada.

GENERAL BOTANICAL CHARACTERISTICS:

Habit: This introduced biennial plant is 1-3' tall. During the 1st year it

consists of a small rosette of leaves, while during the 2nd year it becomes

a little-branched plant about 1-3' tall.

Leaves: The leaves of 1st year plants are up to 2" long and across. They

are cordate-orbicular with margins that are dentate or wavy and their up-

per surface has a reticulated network of veins. The petioles of these basal

leaves are rather long and slender. The alternate leaves of 2nd year plants

have a similar appearance, except that they are usually longer than wide,

spanning up to 3" long and 2" across. The lower and middle leaves along

the stems are usually cordate with blunt tips, while the upper leaves are

often ovate. Both stems and the petioles of 2nd year plants are occasion-

ally hairy, otherwise they are glabrous like the blades of the leaves. The

foliage is often light green or yellowish green in appearance.

Flowers: The upper stems terminate in narrow racemes of white flowers.
While in bloom, these flowers are bunched together toward the top of
the raceme. However, as the flowers mature and develop seedpods, the
raceme becomes more elongated and they become more separated. Each
flower is up to 1/3" across and consists of 4 white petals, 4 light green
sepals, a short cylindrical stigma, and several stamens with pale yellow
anthers. The pedicel of each flower is ¼" long or less.

Fruit/Seeds: The flowers are replaced by elongated seedpods that are call-

ed "siliques." These seedpods are about 1½2" long and narrowly cylin-

drical (although somewhat 4-angled in circumference). Relative to erect

stalk of the raceme, they are spreading and ascending. Each seedpod con-

tains a single row of black oblong seeds.

Roots: The root system consists of a shallow taproot that is white and

branches frequently. This plant often forms colonies by reseeding itself.

REGENERATION PROCESS: Garlic mustard propogates itself by re-

seeding.

HABITAT TYPES: Garlic mustard was introduced into the United
States from Eurasia. Habitats include moist to slightly dry deciduous

woodlands, woodland borders, semi-shaded areas in gardens and along

fence rows, and partially shaded waste areas. This plant rarely strays far

from the shade provided by woody vegetation and it is intolerant of regu-

lar mowing. At the present time, garlic mustard is the worst exotic invader
of deciduous woodlands in the eastern portion of the United States (includ-
ing Sky Meadows State Park) as it has the capacity to crowd out and des-

troy all of the native wildflowers that bloom during the spring. Effective
measures of control include pulling the plants by their roots and spraying
the foliage with herbicides. Cutting the flowering stalks from their stems

is not an adequate method of control because garlic mustard is capable of
regenerating new flowering stalks from its side stems.

SITE CHARACTERISTICS: Garlic mustard prefers partial sun to med-

ium shade, moist to mesic conditions, and a loamy fertile soil. Small
rosettes of leaves are formed during the summer of the 1st year, which die
down to the ground during the winter. However, during the spring of the
following year, new leaves appear on stems that develop rapidly to pro-

duce flowers by early summer. This plant is well-adapted to deciduous

woodlands and can reseed itself aggressively, forming dense stands that

exclude other species. It has few problems with pests and disease.

SEASONAL DEVELOPMENT: The blooming period occurs during

late spring or early summer and lasts about 1-2 months.

GENERAL DISTRIBUTION: Garlic mustard has an unusual distri-
bution. It is absent from all the Gulf states, through the southwestern
states to California. It does occur from most of the southeastern states,
mid-Atlantic states, up through New England and most of the eastern
Canadian provinces (except Newfoundland). It extends west through
the Ohio Valley, into the mid-Prairie states, into the central Rockie

states, and into the northwestern states and provinces. It is absent from

all the Canadian Prairie provinces and the northern Canadian provinces

and territories, but has been reported from Alaska.

SKY MEADOWS DISTRIBUTION: To be determined.

IMPORTANCE AND USES: The flowers attract various kinds of bees
and flower flies. In sunnier areas, the flowers may also attract the intro-
duced butterfly Pieris rapae (cabbage white). Apparently the seeds are
little-used by birds and mammalian herbivores rarely bother the foliage,
possibly because they're repelled by its garlic-like scent. There also
appears to be few native insects that feed on the foliage and other parts
of this plant. Garlic mustard has displaced vast areas occupied by native
spring wildflowers like spring beauty (Claytonia virginica), wild ginger
(Asarum canadense), bloodroot (Sanguinaria canadensis), trilliums
(Trillium species) and toothworts (Cardamine). Three native butterfly
species, the West Virginia white (Pieris virginiensis), mustard white
butterfly (Pieris oleracea), and the falcate orange-tip (Anthocharis
midea annicka), are especially impacted when garlic mustard displaces
toothworts, its host plants. Chemicals in garlic mustard are toxic to the
larvae of the native butterflies. Other chemicals have been found to affect
mychorrhizal fungi associated with native trees, resulting in suppression
of native tree seedling growth. At the present time, ecologists in Switzer-
land are examining the insect pests of garlic mustard in the Old World
to determine if any of them are suitable for introduction into the New
World. Two species of leaf beetles appear to be the best candidates for
biological control.