Glade mallow in flower

Glade mallow (Napaea dioica), a handsome plant of wet prairies and marshes, is the only plant endemic to the north-central United States. On the state species list for Wisconsin, it is listed as of "special concern." Even in the states where it is found, it is rare or threatened. In Wisconsin it is found only in counties in western and southern Wisconsin.

There was already a small glade mallow population at Pleasant Valley Conservancy when we began restoration. As a result of our work creating the Crane Prairie, we now have quite a lot more of this interesting species. We had a good supply of seed (collected locally) when we planted the Crane Prairie in December 2005, which probably explains its present abundance. Now, in its third growing season, we have quite a substantial number of plants, mostly in the wetter part of the prairie. I have been monitoring them since spring and just now they are beginning to flower.

Glade mallow is one of a small fraction of the vascular plant flora that is dioecious, having males and females on separate plants. Both sexes seem to occur in about equal proportions.

According to Cochrane and Iltis, this species grows well in sunny gardens. Because of its tall size it makes a handsome backdrop to a perennial garden.

At one time, the largest population of glade mallow in Wisconsin was found in ditches along U.S. Highway 14 between Cross Plains and Black Earth. Unfortunately, a high-power transmission line also ran along this same area and due to error or ignorance (or both), a contractor hired by the transmission company killed most of the glade mallow plants by spraying the area with the herbicide Tordon. Fortuitously, my wife Kathie was driving past when this spraying operation was in progress. Appalled at what she saw, she waded out into the ditch and was able to convince the contractor to stop further spraying. Her efforts resulted in saving about 30% of this outstanding species. A number of people, including the Wisconsin Department of Transportation, may have learned a lesson here, although whether it will lead to better management of native plant species along our highways is an open question.