Garlic mustard is a cool season biennial herb with stalked, triangular to heart-shaped, coarsely toothed leaves that give off an odor of garlic when crushed. First-year plants appear as a rosette of green leaves close to the ground. Rosettes remain green through the winter and develop into mature flowering plants the following spring. Flowering plants of garlic mustard reach from 2 to 3-½ feet in height and produce button-like clusters of small white flowers, each with four petals in the shape of a cross.
Beginning in May (in the mid-Atlantic Coast Plain region), seeds are produced in erect, slender pods and become shiny black when mature. By late June, when most garlic mustard plants have died, they can be recognized only by the erect stalks of dry, pale brown seedpods that remain, and may hold viable seed, through the summer.
Physical characteristics
Leaf: Simple alternate leaves with toothed edges, deltoid to cordate in shape. 
Flower | Seeds: The flower is radially symmetrical with four small basally connate white petals arranged at right angles. These flowers are generally arranged in clusters.
Seeds are produced in a silique, a dehiscent pod at least three times longer than it is wide. Seeds may be produced by cross-pollination or self-pollination.
Life span: Biennial. Can grow up to three feet in height.
Ecological characteristics
Alliaria petiolata is native to Europe as well as Western and Central Asia. Its range extends from Scandinavia to northern India. Alliaria petiolata was imported to North America for culinary uses, but has since become an invasive species. Its North American distribution extends from the east to west coasts, as far north as Alaska and as far south as Georgia.
Alliaria petiolata can often be found growing near shrubs, brush, and roadsides.
Ecological Threat
Garlic mustard poses a severe threat to native plants and animals in forest communities in much of the eastern and Midwestern U.S. Many native wildflowers that complete their life cycles in the springtime (e.g., spring beauty, wild ginger, bloodroot, Dutchman’s breeches, hepatica, toothworts, and trilliums) occur in the same habitat as garlic mustard. Once introduced to an area, garlic mustard outcompetes native plants by aggressively monopolizing light, moisture, nutrients, soil and space. Wildlife species that depend on these early plants for their foliage, pollen, nectar, fruits, seeds and roots, are deprived of these essential food sources when garlic mustard replaces them. Humans are also deprived of the vibrant display of beautiful spring wildflowers.
Garlic mustard also poses a threat to one of our rare native insects, the West Virginia white butterfly ( Pieris virginiensis ). Several species of spring wildflowers known as “toothworts” ( Dentaria ), also in the mustard family, are the primary food source for the caterpillar stage of this butterfly. Invasions of garlic mustard are causing local extirpations of the toothworts, and chemicals in garlic mustard appear to be toxic to the eggs of the butterfly, as evidenced by their failure to hatch when laid on garlic mustard plants.
Source: United States Department of Agriculture
Importance to the ecosystem
Alliaria petiolata is natively Eurasian. After importation to North America as a culinary herb, it has spread to become an aggressive invasive species that now comprises the dominant understory of many wooded areas.
Its persistence is affected by its ability to grow in dim light and the self-pollinate to produce seeds when no other Alliaria petiolata is available to colonize an area.
Alliaria petiolata may also benefit from the presence of white tailed deer, who do not consume garlic mustard, but will feed on competitors, creating additional space for garlic mustard.
Alliaria petiolata also uses chemical warfare to maintain its dominance by producing allelochemicals that inhibit the presence of mycorrhizal fungi that aid in nutrient assimilation for many plants and trees.
Relationship with other species
Non-human: Alliaria petiolata produces allelochemicals, inhibiting the presence of mycorrhizal fungi that aid in nutrient assimilation for many plants and trees.
It is generally not consumed by non-human animal species, but the native Eurasian Alliaria petiolata serves as a food source for dozens of insects as well as some fungi and the larvae of the the Garden Carpet Moth, Xanthorhoe fluctuata. None of these species are present in North America.
Humans: As its common name, garlic mustard, implies, the leaves of Alliaria petiolata have the scent of garlic while its root bears a taste resembling horseraddish. Both of these characteristics make garlic mustard a useful inclusion in salads, pestos, and other savory dishes.
Pests: Alliaria petiolata has no native pests in North America, but is consumed by dozens of insects in Eurasia, which helps keep the garlic mustard population in check, while serving as a boon to a variety of pest species.
Other interesting facts
- Alliaria petiolata was once used as a disinfectant and diuretic.
- Garlic mustard was first recorded in the United States about 1868, from Long Island, New York. It was likely introduced by settlers for food or medicinal purposes.
- Because the seeds of garlic can remain viable in the soil for five years or more, effective management requires a long term commitment. The goal is to prevent seed production until the stored seed is exhausted. Hand removal of plants is possible for light infestations and when desirable native species co-occur.
References:
Page drafted by Julia Giza
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