Wetlands are ecological zones that are in constant flux, and because of their changing state they are a perfect home for plant species that like to colonize disturbed areas. Vigorous exotic plants that colonize disturbed areas are often called invasive species for their propensity to take over a space, preventing other plants from growing.
Scotch Broom is a Tough, Shrubby Invasive
Scotch broom (Cytisus scoparius) is one tough shrub. This shrub blooms in the hills of Scotland. It frequents open and disturbed areas, where it takes nitrogen from the air and moves it into the soil. Although this is a useful ecological function, broom is very tough and hard to cut or remove and will take over from other local wetland shrubs. You will recognize it by its long, thin stems, brilliant yellow flowers, and seed pods that look like legumes.
The seed pods of Scotch Broom split abruptly, forcing the seeds out and spreading them. Birds and insects can also move the seeds from place to place. People have moved Scotch Broom around by planting it in the garden or simply by walking through an area that is covered with broom, moving the seeds out on shoes and clothing.
Himalayan Blackberry is Delicious But Invasive
Himalayan blackberries (Rubus discolor) are delicious and beloved of many, but they can also form a thicket of branches over a wetland site. Their presence is controversial. They provide food for bears and other animals and provide dense, thick homes for local birds. However, the Himalayan Blackberry can easily take over an area, shading out local shrubs and small plants. Blackberry branches root easily, so take care that you do not leave them beside a pond or a wetland. Blackberries have five oblong, toothed leaves on a thorny stem.
Japanese Knotweed is an Invasive Species in Wetland Areas
You’re walking in a wetland area and you come across a beautiful grove of bamboo, but it has oval-shaped leaves. Wait! This is not bamboo, it’s Japanese Knotweed (Fallopia japonica or Polygonum cuspidatum), and it’s an invasive species that loves to live where it is wet. The rhizomes or roots are tough and can even move through asphalt. Knotweed forms a dense forest of bamboo-like shoots that shade out all other plants.
Purple Loosestrife Loves to Invade Wetlands
Purple loosestrife (Lythrum salicaria) is a beautiful ornamental plant with a stalk of purple flowers. It seems like the perfect plant for a wetland garden, but it will invade the wetland, growing over all plants in damp areas. Wetlands are home to many invertebrate and bird species, and this plant takes over and destroys their food and habitat areas.
English Ivy Climbs on Trees, Shrubs, and the Ground
English ivy (Hedera helix) is a nuisance plant that will cover just about any available surface, shading out other plants. It will even climb and cover large trees. Like many invasive species, ivy can reproduce by rooting from a segment, so that means it is very hard to remove. Brought to North America by homesick Britons, it’s attractive indoors but will take over outdoors. This plant has lobed, triangular leaves.
Recognizing invasive species is a first step to avoiding problems in the wetland or wetland garden. While many invasive species are beautiful or useful in some way, their benefits are far outweighed by their drawbacks, since they will take over from other plant species and can reduce habitat and food sources for local animals.
Tricia Edgar - Tricia Edgar is a gardener, environmental educator, and science writer from the Pacific Northwest.
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