White turtlehead (Chelone glabra, Scrophulariaceae) is a native plant found in wet areas throughout eastern North America (Brandenburg 2010). I came across this individual last week in the wetlands of Pinckney State Recreation Area near Chelsea, Michigan.
This plant features a tall spike of large white flowers that bloom from late summer into autumn. Since I caught this plant early in its flowering period, only one was fully open. The flowers do indeed resemble turtle heads:
White turtleheads produce chemicals known as iridoid glycosides that make them unpalatable to most herbivores (Bowers, Boockvar, and Collinge 1993). As is often the case in nature, however, some herbivores have adapted to feed on it. Checkerspot butterflies (Lepidoptera: Nymphalidae: Euphydryas spp.) in particular feed primarily on turtleheads, and in doing so become unpalatable themselves (Bowers 1981). They also exhibit bright warning coloration to alert predators to their distasteful flavor.
Bowers, M.D. 1981. Unpalatability as a Defense Strategy of Western Checkerspot Butterflies (Euphydryas Scudder, Nymphalidae). Evolution 35(2):367-375.
Bowers, M.D., K. Boockvar, and S.K. Collinge. 1993. Iridoid glycosides of Chelone glabra (Scrophulariaceae) and their sequestration by larvae of a sawfly, Tenthredo grandis (Tenthredinidae). Journal of Chemical Ecology 19(4):815-823.
Brandenburg, D.M. 2010. National Wildlife Federation Field Guide to Wildflowers of North America. Andrew Stewart Publishing, Inc., New York, NY.