Wetlands Invader

Ever wonder what that tall plant with a feathery-tufted top is that you see growing along our roadside ditches? It’s called common reed (Phragmites australis), and in recent years this highly invasive plant has spread through the Chicago region at an alarming rate. Because the reed grows up to 15 feet high, can be very densely populated, and has a tenacious rhizome (underground stem) network, it is a threat to native wetland vegetation and ecosystem function because it physically excludes native species and alters nutrient cycling.

Looks can be deceiving—the common reed appears innocuous enough; in fact, to the naked eye, it is almost identical to native Phragmites that have been part of the North American landscape for some 40,000 years. Native Americans in the southwest used the fibrous native plant in woven mats, musical instruments, and weapons. The fast-spreading European strain likely crossed the Atlantic accidentally aboard ships in the 1800s. Like the colonists, Eurasian Phragmites first established themselves along the Atlantic coast and then spread across the continent.

A Spreading Troublemaker

Here in the Midwest, the common reed began causing trouble 15 to 20 years ago. Once it moves in, it anchors itself with an extensive and unyielding underground network—this is how it grows and spreads—which makes it especially hardy and difficult to eradicate. Common reed invades quickly. It takes over space where native plants would grow, blocks sunlight, and since the plant does not decompose quickly (it stands as dead matter over the winter), it alters the fragile wetlands balance for native fish and wildlife, many of which cannot survive.

Distinguishing Native from Exotic Phragmites

It is very difficult to distinguish the two just by visual observation, but subtle differences do exist between native and exotic Phragmites. The ligule is the inner part of a leaf where leaf meets stem. If you look very closely, the native plant’s ligule is slightly wider than the exotic’s. The chaff of the native plant is slightly longer than that of the exotic, and while the leaves of the native plant will easily fall off the native plant as it dies, the leaf sheath will adhere pretty tightly to the exotic.

Investigating the Culprit

In an effort to understand these plants better and to halt the spread of invasive species, the Chicago Botanic Garden is investigating the genetic characteristics of both native and exotic Phragmites, determining the potential for hybridization between the two in order to provide land managers with valuable information as they rid imperiled wetlands of this aggressive plant.