In over 3 decades of botany here in the upper midwest, TPP has seen blue cohosh (Caulophyllum thalictroides) in the wild exactly twice. As the specific epithet suggests, the thrice compound foliage looks quite like the leaves of the meadow rue (Thalictrum, in the buttercup family). Blue coshosh might be a bit more common that suspected, but it tends to escape notice. Appropriately enough one hides in our woodland behind a screen of bluebells. One of the reasons it escapes notice is that it's purplish-blue hue tends to help it hide. What confuses quite a few people is that the flowers are 3-parted and the same greenish, bluish color as the foliage, however three-parted flowers are common enough among basal dicots. It's a member of the Berberidaceae, and most of the members of the family with which people are familiar are shrubs rather than spring ephemerals. Blue cohosh has quite a reputation as a medicinal plant and was widely used by native americans as an abortive agent atesting to its toxicity, which may explain why it's one thing the bun-buns don't eat.