Cimicifuga (now considered Actea) is a genus of between 12-18 species in the Ranunculaceae, or buttercup family, native to temperate regions of the Northern Hemisphere. Many disagree with the inclusion of Cimicifuga in Actea (baneberry) due to the fact that Actea produces its seed in berries as the common name implies while Cimicifuga produces seed in a dry follicle. Other taxonomists say that is not enough to separate the genera.
Cimicifuga elata (syn. Actea elata) is commonly called tall bugbane. It is an at-risk species native to the Pacific Northwest in the US. It is tall, reaching nearly two meters, and has "maple like" leaves. The flowers come in a branched panicle, each with five white or pinkish sepals, no petals.
Cimicifuga racemosa (syn. Actea racemosa), commonly known in English as bugbane or back cohosh, grows from a horizontal branched dark brown to grayish black rhizome, with tall spires of fragrant, tiny white flowers in early summer over mounds of finely-cut, fanlike green leaves. The flowers actually lack petals; the numerous stamens create the appearance of a white flower spike. The leaf morphology is variable, ranging from pinnately compound to tripinnately compound. It grows well in shade to part sun. Some of the special varieties with dark leaves are best planted in a sunny place where they will get afternoon shade to bring out the color. Black Cohosh, made from the rhizomes, is an important medicinal herb to herbalists (and in the past, Native Americans) and is being explored today as a possible ingredient in cancer treatment.
Cimicifuga simplex (syn. Actea simplex, Cimicifiga ramosa), native to Japan and surrounding regions, grows to just over a meter and is similar in appearance to C. racemosa, but flowers in late summer. The epithet, Cimicifiga ramosa refers to this species, but is an invalid name. The pictures from Martin Bohnet show the dark leaved form 'Brunette', which also developes a pink tinge after a few days of flowering.