Upland boneset, a Special Concern species

Upland boneset (Eupatorium sessilifolium) is a Special Concern species in Wisconsin. We had a small native population when we began savanna restoration. Although it is found throughout eastern North America, it is relatively uncommon wherever it is. It is classified as Threatened in Michigan and Minnesota and Endangered in New Hampshire and Vermont. In our part of the country it is a savanna specialist, and is found in only a few counties in western and southern Wisconsin. Its rarity is indicated by its coefficient of conservatism of 9. The only Dane County collections at the U.W. Madison Herbarium were made in the 19th century.

There is another species, tall bonset (Eupatorium altissimum), and the two species are often found growing together. However, tall boneset is much more common and is found in dry and mesic prairies as well as savannas. We have lots of tall bonset, and although not real common in Wisconsin, it is not considered a rarity.

The key difference between these two species is the leaf structure. Upland boneset has a "sessile" leaf, that is, without a petiole, as the photo here shows. The leaf of tall boneset has a petiole.

Initially we had only a single small population of upland boneset consisting of five plants, all in a single location in our bur oak savanna. As we have restored that area (removing lots of honeysuckle, buckthorn, and weeds) the population has gradually expanded. Today I counted 50 plants, a substantial and satisfying increase.

We have attempted to establish this species at other locations on the Conservancy, by raising plants from seed and transplanting them to other places. However, seed viability has been low, and from a large seeding we have generally obtained only one or two plants for transplant. Plants that we have transplanted have done well, usually flowering the first year. One transplant made three years ago has now increased to five stems.

These modest successes encourage us to keep trying. Perhaps one year we will get a good viable seed crop and will be able to get this interesting species more widely established.