invasive plants

Invasive plants are defined as those that are not native to North America, have naturalized in the environment, and are harmful to native ecosystems. There are plenty of plants—like Queen Anne’s lace—that are not native, but live in relative harmony with native plants.

Invasives, on the other hand, outcompete and ultimately kill native plants.  Why is that bad?  Isn’t one green plant as good as another?

Actually, native plants support much richer food webs.  Oak trees, which are native in North America, support 500 species of moth and butterflies. While Norway Maples, a widely planted city tree, host no moths (or close to none). To birds a Norway Maple is a food desert; while an oak tree is a feast.

Two invasive species that the Mystic River Watershed Association works to remove include Oriental Bittersweet and Water Chestnut.

Oriental Bittersweet

Photo: Erica Wood

Photo: Erica Wood

The case against Oriental Bittersweet is simple: it kills trees. Oriental bittersweet (Celastrus orbiculatus) is a leafy, climbing woody vine and was introduced to the eastern United States in the mid-1800s. It is native to China, Japan and Korea.  Stems of older vines can be up to 4 inches thick and climb over 60 feet. As Oriental bittersweet grows, it chokes or girdles the plant that it is clinging to, shades out other plants and makes trees top-heavy, making them susceptible to wind and ice damage.

Its leaves vary widely in shape and can be round, oblong or teardrop shaped with finely toothed margins and sometimes a long, tapering point. Leaf length ranges from 2-5 inches long and 2-3.5 inches wide. They are glossy green in spring and summer, becoming golden yellow in late summer and fall. It is easily identifiable in the fall by its red and orange berries.


Photo: Erica Wood

Photo: Erica Wood

Water chestnut (Trapa natans) is native to Asia, Europe and Africa. It was introduced in 1897 by a Harvard botanist as an ornamental plant in Fresh Pond in Cambridge.  Water chestnuts spread over the rivers surface, crowding out native plants and altering the water chemistry. In the fall when the plants die, their decomposition draws down the dissolved oxygen which fish and other aquatic animals need to survive. Additionally, the plants get caught in motor boats and limit the use of the river. If we don’t remove water chestnuts, they will literally take over the fresh water portion of the Mystic River! The plant has a floating rosette of leaves with spiky seeds, or nuts, just beneath the leaves.

It’s important that we pull these plants before they have a chance to reproduce so that we diminish the seed bed. You can learn about volunteering with our invasive species removal program below: