If you see an 'Obedient Plant' with much smaller flowers than usual, particularly in northern Illinois, there is a good chance that this is the species you are looking at. The foliage of Western Obedient Plant is very similar to the more common Physostegia virginiana (Obedient Plant); these two species differ primarily in the length of their flowers (about ½" for Western Obedient Plant versus 1" for Obedient Plant). Outside of Illinois, there are some additional Physostegia spp. with similar flowers. They often have floral racemes that are less dense (their flowers are more widely spaced) than the preceding 2 species, or their leaves may have slender petioles and/or blunt teeth.