Buttercup family (Ranunculaceae)
Description: This native perennial wildflower is 3-7' tall. The stems are light green and hairless, while the large compound leaves are bipinnate or tripinnate with 10 or more leaflets. Usually 3 or 5 leaflets are grouped together in the ultimate partitions of each compound leaf. Individual leaflets are up to 4" long and 3" across; they are medium green, glabrous, and lanceolate to broadly ovate in shape. The margins of these leaflets are coarsely toothed; the terminal leaflets are often shallowly to deeply cleft.
Each plant produces one or more panicles of racemes about 1-3' long. These panicles are very narrow and produce only a few secondary racemes around the central raceme. The racemes are narrowly cylindrical in shape and erect; they are densely covered with flowers, buds, and fruits (follicles) in varying stages of development (buds on top, flowers in the middle, and fruits below). Individual flowers span about 2/3" across and they are completely white, consisting of about 24 stamens, a single pistil, and insignificant sepals that drop early. The slender stamens are long and conspicuous, while the pistil has a short curved tip. Each flower has a short pedicel. The blooming period occurs during early to middle summer and lasts about 1½ months. The flowers have an odd unpleasant scent. Each flower is replaced by a small follicle about 1/3" long; this follicle has a beak that is very short and usually curved. Each follicle splits open along one side to release several seeds; these seeds are fairly smooth (not conspicuously scaly). The root system is rhizomatous and fibrous.
Cultivation: The preference is partial sun to medium shade, mesic conditions, and a rich loamy soil with abundant organic material. This plant requires plenty of space.
Range & Habitat: Black Cohosh is rare in Illinois and state-listed as 'endangered.' It has been found in only a few counties in northern and southern Illinois. At some of these localities, Black Cohosh is probably extirpated because it hasn't observed since the late 19th century. At other localities, the population consists of plants that have been introduced. Habitat includes mesic deciduous woodlands (where Sugar Maple is often dominant) and the bases of bluffs along rivers. In Illinois, Black Cohosh is more common in flower gardens than the wild; it is also more common in natural areas further to the east, including the Appalachian mountains.
Faunal Associations: The flowers provide both nectar and pollen to insect visitors. Unfortunately, these insects are largely unknown, in part because Black Cohosh is uncommon in Illinois and neighboring states. The caterpillars of the butterfly Celastrina neglecta major (Appalachian Azure) feed exclusively on Black Cohosh; however, this insect doesn't occur in Illinois. It is doubtful that mammalian herbivores feed on this wildflower to any significant degree because the foliage is toxic.
Photographic Location: A flower garden at The Arboretum in Urbana, Illinois.
Comments: This is one of the largest woodland wildflowers. Black Cohosh is attractive as a wildflower in part because it produces showy spikes of white flowers during the summer, when there is little else in bloom in wooded habitats. For this reason, it's a pity that this species isn't more common within the state. There are two other species that Black Cohosh can be confused with. One of them, Cimicifuga rubifolia (Appalachian Bugbane), has leaflets up to 10" long and across that often display a maple-leaf shape; it also has fewer than 10 leaflets per compound leaf. In contrast, Black Cohosh has smaller leaflets (up to 4" long and 3" across) and there are usually more than 10-20 leaflets per compound leaf. Another species, Cimicifuga americana (American Bugbane), has foliage that is nearly identical to that of Black Cohosh. However, American Bugbane has several pistils in the center of each flower, while Black Cohosh has only a single pistil per flower. Similarly, American Bugbane produces its follicles in clusters (one for each pistil), while Black Cohosh produces its follicles individually.