Cimicifuga racemosa
Cimicifuga racemosa (Black cohosh, Black bugbane or Black snakeroot or Fairy candle; syn. Actaea racemosa) is a member of the family Ranunculaceae, native to eastern North America from the extreme south of Ontario south to central Georgia, and west to Missouri and Arkansas. It grows in a variety of woodland situations, and is often found in small woodland openings.
It is a glabrous herbaceous perennial plant, producing large, compound leaves from an underground rhizone, growing 0.25-0.6 m (7-18 in.) tall. The basal leaves are up to 1 m (39 in.) long and broad, tripinnately compound, the leaflets with a coarsely toothed margin. The flowers are produced in late spring and early summer on a tall stem, 0.75-2.5 m (22-99 inches) tall, in racemes up to 50 cm (20 in.) long; they have no petals or sepals, only a tight cluster of 55-110 white stamens 5-10 mm long surrounding the white stigma. The flowers have a distinctly sweet smell. The fruit is a dry follicle 5-10 mm long containing several seeds.
Although Blue Cohosh (Caulophyllum thalictroides) is similarly named, it is actually a plant in a separate genus.

# Herbal use
Black cohosh has been included in herbal compounds or dietary supplements marketed to women as remedies for the symptoms of premenstrual tension, menopause and other gynecological problems. However, a recent study published in Annals of Medicine (December 19, 2006)casts serious doubt on its efficacy. The researchers actually found black cohosh slightly less effective than a placebo and concluded that the herb "shows little potential as an important therapy for relief of vasomotor symptoms."  However, that study used a product that contained 5 mgs of the active component a day whereas the current daily recommended dose of the long-used standard Remifemin contains 2 mgs. The American Botanical Council discusses that study.  
It was thought that black cohosh contained estrogen-like chemicals, but recent research suggests that it works by binding to serotonin receptors.     Native Americans used black cohosh to treat gynecological disorders and other disorders as well, including sore throats, kidney problems, and even depression.
Black cohosh has been used as an abortifacient (see side effects).

# Side effects
Black cohosh should not be used during pregnancy or lactation. There is a case report of neurological complications in a postterm baby after labor induction with a mixture of black cohosh and blue cohosh (Caullophylum thalictroides) during a home birth. Other cases of adverse outcomes experienced by neonates born to women who reportedly used blue cohosh to induce labor have been published in peer-reviewed journals.
Black cohosh produces endometrial stimulation. Since black cohosh increases blood flow to the pelvic area, its use is not recommended during menses as it may increase or prolong bleeding. Because of the possible estrogenic action, it should be used with caution after six months. Additionally, black cohosh contains tannin, which inhibits iron absorption. This, considered with possible effects of enhancing menstrual bleeding, gives good cause to monitor iron stores when taking black cohosh.
No studies have been published on long-term safety in humans. However concerns arise that, in humans, because of its estrogen-like effects, long-term use may promote metastasis of estrogen-sensitive cancer tissue via stimulation of cells in the endometrium or breast. Black cohosh increased metastasis of cancer to the lungs (but did not cause an increased incidence of breast cancer) in an experiment done on mice (which was never published and the lung tumors were never biopsied, just observed.)NIH.pdf
The liver damage reported in a few individuals using black cohosh has been severe, but large numbers of women have taken the herb for years without reporting adverse health effects.  See the NIH link above for thorough discussion of the liver issue. While studies of black cohosh have not proven that the herb causes liver damage, Australia has added a warning to the label of all products containing black cohosh, stating that it may cause harm to the liver of some individuals and should not be used without medical supervision.
Aside from pregnancy complications, increased menstrual bleeding, anemia, and rare but serious hepatic dysfunction, reported direct side-effects also include dizziness, diarrhea, nausea, and occasional gastric discomfort. Additional possible side effects include headaches, seizures, vomiting, sweating, constipation, low blood pressure, slow heartbeats, weight problems.

# Garden use
Cimicifuga racemosa grows in dependably moist, fairly heavy soil. It bears tall tapering racemes of white midsummer flowers on wiry black-purple stems, whose mildly unpleasant, medicinal smell at close range gives it the common name 'Bugbane'. The drying seed heads stay handsome in the garden for many weeks. Its burgundy, deeply cut leaves add interest to American gardens, wherever summer heat and drought do not make it die back, which make it a popular garden perennial.