Illinois Exotic Species:
garlic mustard Alliaria petiolata

Garlic mustard is native to Europe. It was introduced to the United States in the late 1800s and has spread north to Canada, south to North Carolina and Kentucky, and west to Kansas and North Dakota. In Illinois, it is common in the northern one-half of the state and occurs south to a line from Calhoun to Clark County, with a local occurrence in Jackson County in southwestern Illinois. This species occurs most frequently in upland and floodplain forests, savannas and along roadsides. It invades shaded areas, especially disturbed sites, and open woodlands. It is capable of growing in dense shade and in areas receiving full sun. Garlic mustard is capable of dominating the ground layer in many areas. It is a severe threat to many natural areas because of its ability to grow to the exclusion of other herbaceous species.

Garlic mustard produces a garlic-type odor from all parts of the plant. A plant may growto four feet tall. Basal leaves are kidney-shaped while stem leaves are sharply-toothed, triangular and alternate. This plant has a two-year life cycle. Seeds germinate in early spring, young plants overwinter as basal rosettes, and adults bloom from May through June the following year. Numerous small white flowers are borne at the apex of the stem, and also at some leaf axils. Plants usually produce one flowering stem but may have as many as 10 stems from a single root. Each flower is composed of four white petals that narrow abruptly at the base. Each plant dies after producing seed. Seeds disperse when the long, slender capsules burst at maturity in August. Seeds have a 20 month dormancy period and do not germinate until the second spring after ripening. Garlic mustard has a white slender taproot, with a characteristic "s" shape at the top of the root, just below the base of the stem.

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