Synonyms

Eupatorium sessilifolium var. brittonianum

  Basis for Listing

Eupatorium sessilifolium 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. 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. Not only is this species very rare in Minnesota and adjacent states, but also its oak woodland habitat is 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 is similar in habit to other members of this genus, but can be distinguished from them using the following combination of characters. The flower heads are discoid, and have about 5 perfect flowers on a naked receptacle. The pappus is a single row of slender bristles, and the phyllaries are pubescent with blunt or rounded tips. The leaves are opposite, glabrous, toothed, and lanceolate, with long, sharp tips and rounded sessile bases.

  Habitat

In Minnesota, E. sessilifolium is found in well drained, dry to mesic open oak woods on bluff tops or slopes, often bordering openings or prairie remnants. The known populations consist of only a few plants in each location.

  Biology / Life History

Eupatorium sessilifolium is an insect-pollinated perennial. It reproduces only by seeds, which are dispersed by wind. Plants from Minnesota, Wisconsin, and Iowa belong to the northern populations of E. sessilifolium that differ from southern populations in having pubescence on the upper portion of the stem, and have been segregated as variety brittonianum.

The best time to search for E. sessilifolium is during the flowering period, from August to September.

  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.

  Conservation Efforts in Minnesota

The Minnesota DNR County Biological Survey has been completed within the range of E. sessifolium in the state. As of 2008, no known conservation actions had been undertaken on behalf of this species.

  References and Additional Information

Hartley, T. G. 1966. The flora of the Driftless Area. Dissertation, University of Iowa, Iowa City, Iowa. 931 pp.

Johnson, M. F., and H. Iltis. 1963. Preliminary reports on the flora of Wisconsin. No. 48 Compositae I - Composite Family. Transactions of the Wisconsin Academy of Science Arts and Letters 52:255-342.

Minnesota County Biological Survey. 1994. Natural communities and rare species of Houston County. Biological Report No. 50. Minnesota Department of Natural Resources, St. Paul, Minnesota.

Minnesota County Biological Survey. 1994. Natural communities and rare species of Winona County. Minnesota County Biological Survey Biological Report No. 49. Minnesota Department of Natural Resources. St. Paul.

Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis, Minnesota. 320 pp.