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Spotted knapweed

Spotted knapweed is an aggressive, introduced weed species that rapidly invades pasture, rangeland and fallow land and causes a serious decline in forage and crop production. The weed is a prolific seed producer with 1000 or more seeds per plant. Seed remains viable in the soil five years or more, so infestations may occur a number of years after vegetative plants have been eliminated. Spotted knapweed has few natural enemies and is consumed by animals only when other vegetation is unavailable. The plant releases a toxin that reduces growth of forage species, so areas heavily infested with spotted knapweed often must be reseeded once the plant is controlled.

Historical records indicate that spotted knapweed was introduced from Eastern Europe into North America in the early 1900s as a contaminant in crop seed, it now infests several million acres.

Honeysuckle

Honeysuckle (Lonicera) is one of the plants that will invade a habitat if it is protected from fire. Most honeysuckles are upright shrubs ranging from a few feet to 15 feet tall. They form many branches from the base, and the spreading branches shade other plants. In a honeysuckle "thicket", almost nothing will be found under the canopy. (After the honeysuckle is removed, the soil is often bare.) Honeysuckles form fragrant tubular flowers, followed later by red fruits. Birds are attracted to the fruits and spread the seeds. Bush honeysuckles have a wide tolerance, but they prefer partial to full sunlight and are most commonly found in abandoned fields, forest edges, roadsides, and other open upland habitats. They are extremely invasive and can easily take over and dominate a habitat.

Buckthorn

Buckthorn (Rhamnus cathartica) first came from Europe in the mid-1800s as a very popular hedging material. Shortly after its introduction here, it was found to be quite invasive in natural areas because it lacks natural controls like insects or disease to curb it’s growth, allowing it to form an impenetrable layer of vegetation. The nursery industry stopped selling it in the 1930s, but many buckthorn hedges may still be found in older neighborhoods.

This invasive species out-competes native plants for nutrients, light, and moisture; it degrades wildlife habitat and threatens the future of forests, wetlands, prairies, and other natural habitats.

Phragmites

Phragmites, also known as common reed, is a member of the grass family. It grows in dense monotypic stands and can reach 15 feet in height. While phragmites is native to Michigan, an invasive non-native variety of phragmites is becoming widespread and has the ability to dominate ecosystems ranging from uplands to wetlands, including the Great Lakes coastal shorelines.

The rapid expansion of this invasive plant is displacing the native variety of the same species, as well as many other native species, thus reducing both plant and animal diversity in the process.

Dame’s Rocket

Dame’s Rocket, Sweet Rocket, or Dame's Violet (Hesperis matronalis) is an attractive, but invasive plant. A common garden flower introduced to America from Europe in colonial times, it is invading woodlands and has the potential to become ecologically devastating to native plant species.

Dame's rocket is listed as a noxious weed by the United States Department of Agriculture. This weed in the mustard family has many similarities with garlic mustard, a related plant that has inundated woodlands in the state in recent years. Dame's rocket has been around for many years, but seems to be showing up in more and more sites all the time; it is now at a relatively early stage of encroachment.

This old-fashioned, cottage garden perennial reaches 3-4 feet tall and has showy flowers that last for several weeks. It is short-lived, but a prolific self-seeder that has escaped cultivation and adapted throughout most of the United States.. Outside of gardens, it is found along roadsides, woodland edges, and is increasingly moving into good quality forests where it can shade out native wildflowers.

Garlic mustard

Garlic mustard is a cool-season biennial herb that ranges from 12 to 48 inches in height as an adult flowering plant. Leaves and stems emit the distinctive odor of onion or garlic when crushed (particularly in spring and early summer), and help distinguish the plant from all other woodland mustard plants. It is rapidly spreading and displacing native woodland wildflowers in Michigan. It dominates the forest floor and can displace most native herbaceous species within ten years. This plant is a major threat to the survival of Michigan's woodland herbaceous flora and the wildlife that depend on it. There are two modes of spread: an advancing front, and satellite population expansion possibly facilitated by animals. Unlike other plants that invade disturbed habitats, garlic mustard readily spreads into high quality forests.

Purple Loosestrife