Our wetlands are vital habitats, but a singular plant species is threatening their quality in many places across Illinois and elsewhere in the United States.

Phragmites, also called common reeds, are those tall wispy grasses that surround many of our wetland areas. While they may seem like a normal part of our wetlands, they aren't native and pose serious threats to the health of the ecosystems where they become established. 

Non-native phragmites, Phragmites australis, were originally introduced in the eastern United States in the early 1800s, and they have slowly expanded to the west over the ensuing decades and centuries, according to the Michigan State University Extension. Once established in a wetland, it can grow in dense stands that crowd out other plants. They spread through windblown seeds, seed transfer from animal activity and the spread of their underground rhizomes. 

The older a population of phragmites is, the harder it is to manage and control because its rhizome system spreads and becomes firmly established, the Michigan State extension reports. 

Because phragmites crowd out other plants, they lessen biodiversity, the Connecticut Agricultural Experiment Station reports. The more dominant the phragmites become, the less room there is for other species. And it's not just native plants that get pushed out. Fish and other wildlife species are also affected. Even our own enjoyment of wetland areas is diminished by the reeds because the waterways are less viable for fishing and swimming, and it even increases the risk of wildfires.

In the Midwest, non-native phragmites began causing problems in wetland areas about 20 years ago, according to the Chicago Botanic Garden. Within the Will County preserves, the invasive plant has become a problem throughout the Rock Run corridor, especially Lower Rock Run and the southern portion of Theodore Marsh, said Andy Hawkins, the District's director of conservation programs.  

Other preserves have also had problems with phragmites, although regular maintenance has helped limit the spread, Hawkins said. In particular, at Braidwood Dunes and Savanna Nature Preserve, Lockport Prairie Nature Preserve and Romeoville Prairie Nature Preserve, District crews work actively and aggressively to keep phragmites and cattails out of the wetlands. In these places, the seeds of the plants are still present, so ceasing the management practices would allow the phragmites and cattails to return. 

The invasive phragmites plants that are populating our wetlands are very similar in appearance to a native phragmites that have grown in the United States for tens of thousands of years, according to the Chicago Botanic Garden. Casual observers would have trouble telling the two species apart, but there are clues that can be used to tell the difference between the native and non-native species.

Among the difference between native and non-native phragmites are color and size. The leaves of native phragmites are more of a yellowish-green, while the non-native reeds have deeper, more bluish green leaves, the Connecticut agricultural station reports. The non-native reed also grow much taller, up to 20 feet tall compared with 6 feet or 7 feet tall for the native phragmites.

Within the preserves, native phragmites exist at Rock Run Preserve and possibly a few other wetland areas as well, Hawkins said. Unlike the non-native species, native phragmites is not detrimental to the local ecosystem.