Rare Species Guide

  Synonyms

Eupatorium sessilifolium var. brittonianum

  Basis for Listing

Eupatorium sessilifolium (upland boneset) was proposed for state threatened status in 1984, because it was known from only one location in Minnesota, and it was reported to be declining in other states. Its total range is limited to eastern and central United States. However, it was not listed at that time because too little fieldwork had been done to support any status designation. Since that time, extensive fieldwork has been conducted, which resulted in the discovery of only a few additional small populations, all in the southeast corner of the state (Paleozoic Plateau). Not only is this species very rare in Minnesota and adjacent states, but its oak woodland habitat is also coming under increasing pressure from land uses incompatible with the continued persistence of E. sessilifolium. Consequently, the species was listed as state threatened in 1996.

  Description

Eupatorium sessilifolium usually stands about knee high, or sometimes waist high, and has a flat-topped, branched inflorescence of whitish flowers. The leaves are 7-15 cm (3-6 in.) long, sessile, (lacking a petiole), and are arranged in opposite pairs on the stem. They are ovate in shape with a narrowly pointed tip and a rounded base. The base does not clasp the stem. The surfaces of the leaves are smooth, and the margins are finely toothed. The individual flowers are small, with petals only 3-4 mm (0.1-0.2 in.) long. Each head will have 5 flowers, and each inflorescence will have dozens of heads.

  Habitat

In Minnesota, E. sessilifolium is found in well drained, dry to mesic open oak woods and savannas. It is usually found on bluff tops or south-facing slopes, often bordering openings or prairie remnants.

  Biology / Life History

Eupatorium sessilifolium is an insect-pollinated perennial. Specific pollinators are not known, but the structure of the flowers indicates it is likely pollinated by small bees. It reproduces only by seeds, which are dispersed by wind.

  Conservation / Management

Survey efforts for E. sessilifolium are complicated by our incomplete understanding of its habitat requirements and by the species' superficial resemblance to closely related common species. It has been documented from only a small number of sites in Minnesota, and the oak ecosystems in the southeastern part of the state where it has been found continue to be threatened by development. Surviving habitat remnants are often thickly infested with Rhamnus cathartica (common buckthorn), an aggressive non-native species that invades oak forests and displaces native species. Efforts to restore habitats should begin with hand cutting of invading woody species. Herbicides should be used with care, if at all. Subsequent management should employ dormant season prescribed fire at intervals of 3-5 years.

  Best Time to Search

The best time to search for Eupatorium sessilifolium is when it is in flower, during July and August.  

  Authors/Revisions

Welby R. Smith (MNDNR), 2023

(Note: all content ©MNDNR)

  References and Additional Information

Hartley, T. G. 1966. The flora of the "Driftless Area". The University of Iowa Studies in Natural History Vol. XXI, Number1. University of Iowa, Iowa City. 178 pp.

Johnson, M. F., and H. H. Iltis. 1963. Preliminary reports on the flora of Wisconsin. No. 48. Compositae - Composite family (tribes Eupatorieae, Vernonieae, Cynarieae, and Cichorieae). Pages 255-342 in G. F. Berquist, Jr., editor. Transactions of the Wisconsin Academy of Sciences Arts and Letters. Vol. LII. Wisconsin Academy of Sciences, Arts and Letters, Madison.

Siripun, K. C., and E. E. Schilling. 2006. Eupatorium. Pages 462-474 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 21. Oxford University Press, New York, New York.