Amanda Weise, a botanist with the University of Minnesota, was searching the woods of a Wisconsin state park for rare and endangered plants when instead she stumbled upon a long-feared invasive weed.

Weise’s discovery is the first evidence that Japanese stiltgrass, which can change the makeup of forest floors by strangling out native grasses, flowers, young trees and other plants, has made it to the Upper Midwest.

Weise found a patch of the stiltgrass, which reaches about calf-high and has broad leaves with a telltale white stripe down the middle, growing about 20 miles from the Minnesota border inside the Coulee Experimental State Forest in La Crosse County, Wis.

“My fear is that it may become more widespread,” Weise said.

“Once these invasive plants become more widespread the likelihood of control deeply declines and what seems doable up front just becomes overwhelming.”

The stiltgrass has now been found in virtually every state south and east of Minnesota. It has been slowly working its way across the country since it was introduced in Tennessee in the 1910s.

It’s become prominent and even dominant in parts of Appalachia and New England.

The invasive weed is feared by botanists because it is aggressive and does especially well in wetlands, along rivers and in the shade of forests with rich soils and higher acid levels, where some of Minnesota’s rarest and most endangered plant species are already struggling to hang on.

Weise said it is particularly worrisome that the stiltgrass was found in what would be prime habitat for it — in the rich and bluff-filled corner of Minnesota, Wisconsin and Iowa known as the Driftless Area.

“The Driftless Area is really where we have some of our greatest plant diversity,” she said. “It’s where we see ginseng and goldenseal. These plants that people really value and have medicinal value all overlap in that habitat.”

The stiltgrass doesn’t provide meaningful nutrition for deer, rodents or other animals and offers very little habitat for insects or pollinators.

One of the dangers is that patches of stiltgrass can create a highly flammable fuel source that could feed stronger, more intense wildfires, said Kelly Kearns, invasive plant specialist for the Wisconsin Department of Natural Resources.

As an annual grass, it grows very quickly, covering up other species in a dense patch, Kearns said. By the time the frost comes and kills it off in the fall, the stiltgrass has already spread seeds for the next spring.

“So you have these dense areas of a dead grass that’s climbed over every other thing and now it’s dry and it’s extremely flammable,” Kearns said.

Kearns said she’s hopeful that the patch Weise discovered may have been eradicated. It seems to have been caught particularly early, after only a year or two in the state forest.

Seeds likely hitchhiked to the area on the bottom of someone’s boot or other gear, Kearns said. The patch was found near a parking lot. DNR crews carefully searched all roads, trails and streams and found that it may not have spread far. All patches found were hand-pulled and sprayed.

The DNR will continue monitoring and spraying the area for the foreseeable future in case seeds were carried farther into the woods, Kearns said.

“This was a textbook example of early detection and control, and why citizen reports of invasive species are so important,” she said.

Anyone who finds the invasive grass is asked to map its location and send a picture via e-mail to arrest.the.pest@state.mn.us if found in Minnesota, or to invasive.species@wisconsin.gov if found in Wisconsin.