Upland boneset, a Special Concern species

Upland boneset (Eupatorium sessilifolium) is a Special Concern species in Wisconsin and Threatened in Michigan. As the Wisconsin State Herbarium map shows, it has a narrow distribution in the southern part of the state. It has a Coefficient of Conservatism of 9.

(Although it is a "classic" savanna species, for some reason it was excluded from the Cochrane/Iltis Atlas of the Wisconsin Prairie and Savanna Flora.)

Note that E. sessilifolium can be easily distinguished from the much more common tall boneset (E. altissimum) because of its sessile leaves (see photo below).

In the early days of restoration at Pleasant Valley Conservancy we had only a single stand of 5 stems at the SE corner of Unit 8. We raised seedlings in the greenhouse and planted transplants in likely areas in the Conservancy. Most of these transplants grew and we now have this species in a number of good savanna sites. In addition, it has spread on its own from the original stand and there are now many plants in other parts of Unit 8.

We have been working with upland boneset for over ten years now, and have found that despite the lush flowers and seed heads, germination of seeds is below 5%. However, the species transplants well, so that those seedlings we have been able to raise generally become well established. The population shown in the photos here was part of a transplant series that has flourished in Unit 19C.

This species may be more common in southern Wisconsin than the map below shows. (Because it is a State-listed species, detailed locations are not given in the Herbarium website.)

Update 26 October: Yesterday I discovered a new large patch of upland boneset just south of the South Firebreak in Unit 5. Kathie and I counted over 20 flowering stems. Nice to know this species is spreading on its own.

The sessile leaves are an unmistakable characteristic of Eup-sess.