Ironweed: a wet-mesic species

Ironweed (Vernonia fasciculata) is now in full bloom in our wet-mesic prairies (Barn Prairie, Valley Prairie). This is a species with an intense and distinctive color. It is apparently common in southern and western Wisconsin, although according to the USDA plant index it is absent from most of eastern United States.

Although we planted it in our two wet-mesic prairies, we have a population that we did not plant living along the narrow band of Black Earth Dolomite about half way up the south-facing slope in Unit 6. (This population was apparently here even before we started restoration work.)

What is a wet-mesic species doing up there on the south slope? I assume that there is ground water seepage in this dolomite layer, making conditions favorable for ironweed. Seems reasonable, since there is also a native population of Culver's root (Veronicastrum virginicum), another wet-mesic species, growing on this same dolomite shelf.

I am fascinated by these micro-habitats. This same dolomite shelf was also home to a substantial population of sweet clover that we have now mostly eradicated.