Photo by me, Browns Woods
Part of the aster family.
This plant is poisonous. It has a round stem.
From the Illinois Wildflower webpage for the flower:
The common name of this species derives from the erroneous belief among early settlers [and natives] that the bitter rhizomes were beneficial in the treatment of snakebites. In fact, the foliage and rhizomes are highly toxic, causing fatalities from 'Milk Sickness' because the toxins can pass through the milk of dairy cattle to humans. .... White Snakeroot usually occurs in and around shady woodlands, while many of these other species are found in prairies and sunny wetlands.
Maybe you've read about this milk sickness in places like this Iowa blog or perhaps while visiting the Lincoln Boyhood Memorial.
White snakeroot's native to North America. I've read that it is one of the last flowers to bloom in the fall.
Other than the flowers, I notice the heavily veined leaves.