Upland boneset, an oak savanna specialist

Upland boneset (Eupatorium sessilifolium) is an uncommon but attractive member of the oak savanna understory flora. It has a Conservation Coefficient of 9, and is on the Wisconsin DNR list as Special Concern. Although definitely a savanna species, for some reason it was left out of the Atlas of the Wisconsin Prairie and Savanna Flora.

Initially we had only a single population of this species at Pleasant Valley Conservancy, which consisted of five plants. This population (in Unit 8 near the South Fire Break) has spread extensively since we started annual savanna burns. After five years it had enlarged to over 25 plants. In addition it spread to other areas in the unit, and recently has crossed the walking trail into Unit 19A.

Flowering and seed set were good and we attempted to raise plants in the greenhouse. Unfortunately, seed germination was very low, so we only got a few plants to transplant. However, these transplants became well established and flourished. We have continued to raise new plants yearly and now we have quite a few stands across our ridge-top savanna, primarily in the dolomite areas.

Upland boneset (white flowers) in an area with purple Joe Pye weed and Canada trefoil.

Right now upland boneset is the only species in the savanna with small white flowers and is therefore easy to spot during a walk-through. The sessile leaves are the best identification characteristic. The related species tall boneset (Eupatorium altissimum) is still in bud and its inflorescences are off-white. 

As the distribution map shows, most of the sites in Wisconsin are in the Driftless Area. The single "dot" in Dane County is misleading, since Kathie and I have found quite a few other sites. One of the more interesting is a rather large population in the middle of the prairie in the South Unit at Black Earth Rettenmund Prairie. Should a savanna species be able to thrive in an open prairie? As it turns out, the South Unit at Rettenmund had become fairly wooded during the 50 years of neglect before the Prairie Enthusiasts started restoration work, preumably favoring the development of upland boneset. Quite a few large honeysuckle bushes were removed in the area where the upland boneset now flourishes.

Although the U.S. distribution map for this species shows it throughout the east, it is considered endangered or threatened in a number of states, including Minnesota, Michigan, New Hampshire, and Vermont.