The most pervasive environmental threat may be cloaked in the guise of ordinary and often attractive plants.

Most people aren’t aware of the ecological damage invasive plants are inflicting on our biodiversity, our wildlife and our native plant species.

An invasive plant is defined as a plant that grows aggressively, spreads and displaces other plants in an ecosystem.

A small number of invasive species are native to Pennsylvania, which means they grew in the state before settlement by Europeans.

Most invasive species were brought to Pennsylvania from other continents.

These species are often called alien, exotic, introduced or non-native.

These plants have been introduced into environments where there are no diseases or pests to control them.

They are often silent threats because most people aren’t aware of invasive plants or don’t notice them spreading into a new environment.

Many species now considered invasive originally were introduced intentionally as landscape plants or for other purposes.

Here is a list of invasive plant species commonly found in Pennsylvania ecosystems:

Tree of Heaven - This tree produces a huge number of seeds, which are easily spread by the wind along roadways. It grows very fast, as much as 10 feet in a season, and can grow to more than 60-feet-tall. It spreads new shoots from its extensive root system.

Japanese Stiltgrass - An annual grass that has invaded woodlands across the state. It has been a hindrance to forest regeneration.

Autumn Olive - Introduced as a wildlife cover, the shrub produces large numbers of seeds that are widely spread by birds.

Multiflora Rose - This shrub was also introduced as a wildlife cover. Its seeds are spread by birds. The plant does have a biological control.

Purple Loosestrife - Purple loosestrife invades wetlands and sites that have been disturbed or cultivated. Its seeds are easily transported by animals or vehicles. Its vibrant purple flowers and long growing season make it attractive to uninformed gardeners.

Japanese Knotweed - Also called Japanese bamboo, it easily spreads along rivers. It grows to nearly 10 feet, but provides little cover or food for wildlife. Its spread by seed is limited, but it has an extensive root system, which makes it difficult to control.

Phragmites or Common Reed - Common to wetland areas, the plant has native and introduced varieties. It forms huge colonies, pushing out native plants and wildlife.

Canada Thistle - A weed that spreads by airborne seeds. It creates problems in farm crops.

Mile-a-Minute Vine - It can grow six inches a day, and more than 25 feet in one growing season. It can smother small saplings and seedlings in developing forests or reforested land.

Poison Hemlock - Unrelated to the hemlock trees, this herbaceous plant is what Socrates mixed into a drink to commit suicide. It’s related to water hemlock, which is more poisonous than poison hemlock.

Invasive plants threaten the habitat of two-thirds of threatened and endangered wildlife species.

The best way to control these plants is to familiarize yourself with them and work with local officials and agencies to start eradication programs.

“Growing Green” is contributed by Diane Dorn, Lehigh County Extension Office Staff, and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613