Cirsium palustre: an evasive invasive.

Abstract

In Michigan, the European swamp thistle, Cirsium palustre (L.) Scop., a member of the Asteraceae family, is an introduced species that was transported from western Europe in the early twentieth century, and has since established itself as an aggressive weed. It colonized primarily alkaline wetland habitats, like cedar swamps which are exposed by frequent breaks in cover, and to regions of great disturbance, like roadsides. This introductioin and subsequent invasion has established Cirsium palustre on both sides of the Atlantic ocean in the northern latitudes, a circumpolar species, Figure 1. It was first recognized earlier this century in North America and collected in Newfoundland and New Hampshire. Locally, this invader has spread voraciously from Michigan's Upper Peninsula, where it was first collected in Marquette County in 1934, to the Lower Peninsula where it was assimilated by 1959. It migrates vigorously along roadside ditches and by human transport, and continues to travel south.