Photo credit: © Christophe Quintin, https://flic.kr/p/bEPHDG

Garlic Mustard

(Alliaria petiolata)

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Species at a Glance

Garlic mustard is a cool season biennial herb with leaves that give off a garlicky odor when crushed. First-year plants appear as a rosette of 4-8 green leaves that grow close to the ground and remain green all winter. In the spring, the rosettes develop into flowering plants that quickly dominate the forest floor, threatening native plants and forest communities throughout the Eastern and Midwestern United States.

Identification

Leaves: First-year rosettes have dark green, kidney-shaped leaves with scalloped margins and deep veins that give them a wrinkled appearance. In the second spring, a flower stalk rises from the rosette bearing alternate, triangular to heart-shaped, coarsely toothed leaves that smell like garlic when crushed. These flowering plants reach 0.6-1 m (2-4 ft) in height.

 

Flowers: Clusters of small white flowers appear at the end of an erect stalk on only second-year plants. Each flower has four petals and blooming occurs from late April through June.

 

Fruits/Seeds: Seeds are produced in long slender capsules 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 seed pods that remain throughout summer.

 

Stems/Roots: Single stems are weak and have a white, slender taproot that is “S”-shaped at the top.

Similar Species

Cut-leaved toothwort (Cardamine concatenata), sweet cicely (Osmorhiza claytonii), and early saxifrage (Micranthes virginiensis) are native white-flowered plants that occur in the same habitat and may be mistaken for garlic mustard. Cut–leaved toothwort is low-growing but has narrow, finger-like leaves. Sweet cicely has fern-like leaves and flowers with five petals, and early saxifrage has five white petals.

Habitat

Garlic mustard usually grows in the moist shaded soils of river floodplains, forests, roadsides, edges of woods and trails, and forest openings. It thrives in shady conditions, but can tolerate sunny habitats, usually resulting in smaller flowering plants. Disturbed areas are most susceptible to rapid invasion and dominance.

Spread

A single garlic mustard plant can produce thousands of seeds that can scatter as far as several meters from the parent plant. These seeds can stay dormant for 20 years before germinating and remain viable for 5-8 years. Depending on the conditions, garlic mustard can either self-fertilize or be cross-pollinated by a variety of insects. While water may transport the seeds, they don’t float well and are not carried far by wind; therefore, long distance dispersal is most likely through animals that can carry the seeds in their fur, or through human-mediated pathways.

Distribution

Originally from Europe, garlic mustard was first recorded in the United States in 1868 from Long Island, New York. It was most likely introduced by settlers for food and medicinal purposes. By 1991 it had invaded 28 Midwestern and Northeastern states, and can be found in all states throughout the Mid-Atlantic region.

 

Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.

Environmental Impacts

Garlic mustard aggressively monopolizes resources needed by native plants, such as light, moisture, nutrients, soil, and space. Wildlife that depend on native plants blooming early in the spring are deprived of essential food sources when garlic mustard replaces them, and very few insects, deer, or other herbivores will eat it.

Video
Note

Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).

The Pennsylvania iMapInvasives Program is a partnership of the Western Pennsylvania Conservancy, the Pennsylvania Natural Heritage Program, and NatureServe.

Funding for Pennsylvania iMapInvasives is provided by the Great Lakes Restoration Initiative.

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Pennsylvania Natural Heritage Program, iMapInvasives partner
Great Lakes Restoration Initiative logo, iMapInvasives funding source