Western Obedient Plant
Mint family (Lamiaceae)
Description: This native perennial wildflower is 1½3½' tall and mostly unbranched, except in the upper one-third, where some lateral stems may be produced. The stems are bluntly 4-angled, medium green, and glabrous; the central stem is rather stout and erect. Opposite leaves occur at intervals along these stems, rotating 90° from the pair of leaves below; they are widely spreading, medium to dark green, and glabrous. The leaves are 3-4" long and about ½" across; they are narrowly lanceolate to oblong-elliptic in shape and their margins have widely spaced teeth that are sharply serrated. The base of each leaf is sessile, or nearly so; the upper 2 pairs of leaves may clasp the central stem slightly. The upper stems terminate in spike-like racemes of flowers about 2-6" long. These racemes are erect and they are densely covered with flowers, developing fruits, or buds. Usually, only a few flowers are in bloom at the same time, beginning at the bottom of each raceme. Each flower is about ½" long, consisting of a tubular corolla and a green calyx with 5 broad teeth; the corolla is much longer than the calyx. The 2-lipped corolla is pale purple, lavender, or nearly white. The upper lip consists of a short broad hood, while the lower lip is irregularly divided into 3 short lobes. At the base of each flower, there is a small linear-lanceolate bract that is shorter than the calyx. The blooming period occurs from mid-summer to early fall and lasts about 1-2 months. There is no noticeable floral scent. Each flower is replaced by 4 small nutlets. The root system produces a taproot and rhizomes. This wildflower can spread by reseeding itself, or it may form small colonies of plants from its rhizomes.
Cultivation: The preference is full or partial sun, wet to mesic conditions, and a fertile soil containing sufficient organic matter to retain moisture. Insect pests and foliar disease are rarely troublesome.
Range & Habitat: Western Obedient Plant has been found in only 3 counties in northern Illinois and it is quite rare (see Distribution Map). Illinois lies at the eastern range-limit for this species. Habitats include wet to mesic prairies, damp thickets, and banks of streams and ponds.
Faunal Associations: Little information about floral-faunal relationships is available for this western species, but it is probably similar to Physostegia virginiana (Obedient Plant). Bumblebees and other kinds of bees are undoubtedly major pollinators of the flowers; the Ruby-Throated Hummingbird and some butterflies may visit the flowers as well. Nectar is the primary floral reward of these visitors. The foliage of both Obedient Plant and Western Obedient Plant doesn't appear to be utilized as a source of food to any significant degree by mammalian herbivores.
Photographic Location: A wetland restoration at Judge Webber Park in Urbana, Illinois, where this species unexpectedly appeared. It remains to be seen if this species will persist at this site.
Comments: 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.