Kew Species Profiles
An attractive woodland plant native to Northern America, black cohosh is commonly grown as a garden ornamental in temperate regions. It is the source of several medicines traditionally used by native North Americans as well as early European settlers, and is a globally popular herbal remedy for treating the symptoms of menopause.
It is almost exclusively harvested from the wild, hence black cohosh has been the subject of some concern for conservationists and regulators as the global demand for products containing this herb increases. The popularity of black cohosh is also having an impact on other species of Actaea and similar plants, which are sometimes confused with black cohosh or intentionally substituted by unscrupulous traders.
Black cohosh grows primarily on the moist, fertile slopes of deciduous woodlands along the eastern United States and southeastern Canada. It has a broad distribution, which overlaps with those of several other American Actaea species.
Various species of Actaea , including black cohosh, are cultivated as ornamentals in partially shaded or woodland gardens in temperate regions.
DescriptionOverview: An attractive clump-forming herbaceous perennial that can reach a height of 2 m or more. The plant produces tall, narrow spikes of small, white flowers that have a tendency to bend slightly towards the sun.
Leaves: The leaves are compound (divided into many smaller leaflets). The leaflets are usually mid to dark green and toothed, with 2-5 sets branching out in groups of three along the petiole (leaf stem). Individual plants may have as few as just one or two compound leaves of up to 60 cm in length. Clumps can become sizeable over time.
Flowers: Tall flower stems branch into several long, narrow racemes (flower spikes) of small creamy-white flowers from June to September. These appear as a cluster of stamens (male parts) surrounding the stigma (female part) with no petals or sepals apparent. They have a mildly foetid smell that attracts flies as pollinators.
Fruits: Black cohosh produces what are known as follicles, on short stalks along the flower stem. These are dry fruits that develop from each flower and split open across the top and down one side to reveal the seeds.
Seeds: Each follicle contains two rows of tiny, smooth, brown seeds - similar in shape to the segments of an orange.
Actaea or Cimicifuga?Swedish botanist Carl Linnaeus published the name Actaea racemosa in Species Plantarum in 1753.
On noting the marked difference between the dry follicles produced by black cohosh and the bright fleshy fruits of some other Actaea species, British-American botanist Thomas Nuttall moved this plant to the genus Cimicifuga in 1818.
There it remained, as Cimicifuga racemosa , until 1998 when scientists studying the entire group concluded that, in spite of the differing fruits, the genera Actaea and Cimicifuga are so genetically similar that they should not remain separate.
Hence black cohosh is often known by the synonym Cimicifuga racemosa , which was considered the correct scientific name for this species until relatively recently.
Threats and conservationFor medicinal purposes it is usually the rhizome (underground stem) of black cohosh that is used and so the entire plant must be dug up in order to harvest the medicinal part. Black cohosh is almost exclusively harvested from the wild, and global demand has been increasing over time with over 40 million plants harvested for the international marketplace between 2000 and 2010. To add to this, plants grown from seed can take as long as three to four years before they flower and even longer before the rhizome reaches a reasonable size for harvesting, which places a further strain on wild populations and makes cultivated black cohosh products more expensive.
Although not currently listed on the IUCN Red List of Threatened Species, black cohosh has been the subject of ongoing monitoring by the United States Fish and Wildlife Service and the US Forest Service due to reports that local populations are in decline. Growing international trade has been identified as the primary threat, although habitat loss may also be an issue in some areas. In particular, reports suggest that black cohosh is threatened in the states of Massachusetts and Illinois, but limited data regarding other regions, as well as inconsistencies in data collection over time, means further assessment is required for Actaea racemosa in order to safeguard its future.
A proposal to include Actaea racemosa in Appendix II of CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora), which aims to protect species from over-exploitation, was rejected in 2002 and further review recommended.
Uses Traditional medicineBlack cohosh rhizome was traditionally used by a number of Native American tribes, including the Cherokee and Iroquois, for a broad range of complaints including rheumatism and tuberculosis and as a gynaecological aid.
In modern Western herbal medicine, use of black cohosh is generally limited to treating the symptoms of menopause and other complaints of the female reproductive system, but application across a much broader range of disorders, including arthritis and tinnitus, is still supported by many. Black cohosh was noted as one of the five top selling over-the-counter herbal remedies in the United States in 2013.
OrnamentalBlack cohosh is particularly prized for its clump-forming habit and tall spikes of creamy-white flowers that stand out in a woodland garden setting. It has received a Royal Horticultural Society (RHS) Award of Garden Merit.
CultivationBlack cohosh is fairly easy to grow in a cool, partially shaded border or woodland garden. The soil should be moist with plenty of organic matter, although black cohosh can also be grown in slightly more rocky settings.
The quickest method of propagation is to divide the rootstock of a large clump in early spring, ensuring that each piece of rhizome includes at least one bud. Propagation by seed is also possible, although plants grown in this way will take longer to reach flowering.
Black cohosh at KewBlack cohosh can be seen growing at the edge of Kew's Woodland Garden (near the south end of the Princess of Wales Conservatory).
Several historical and more recent samples of dried black cohosh rhizome are held in Kew's Economic Botany Collection. Specimens like these are often used as benchmarks to aid in the identification, analysis and authentication of herbal products and raw materials found in trade. These samples are available to researchers by appointment.
Preserved specimens of Actaea racemosa are held in Kew's Herbarium where they are available to researchers by appointment. Images of some of these specimens are available online in Kew's Herbarium Catalogue.
Black cohosh and Kew's Medicinal Plant Names Services projectMedicinal Plant Names Services (MPNS) is a Kew project working with herbal regulators, traders and practitioners to clear up confusions surrounding plant names for the broader benefit of the general public.
For example, although black cohosh ( A. racemosa ) is used to treat the symptoms of menopause, three species of Actaea from Asia ( A. cimicifuga , A. dahuria and A. heracleifolia ) are used in Traditional Chinese Medicine for very different complaints, such as toothache and diarrhoea. The problem is that all these species are referred to by the same pharmaceutical name 'Cimicifugae Rhizoma' in some important medicinal literature. In addition, because pharmaceutical names like this one are written in Latin, they can be easily confused with scientific plant names leading to misunderstandings about which species is being referred to.
This poses potentially serious problems in trade and medical practice since it means herbal products with different chemistry are easily mixed-up or misused unless the correct scientific name of the plant involved is included in literature and on labelling. Kew's MPNS are helping the industry deal with problems like these by providing services to link accepted scientific names with as many common, drug and pharmaceutical names as possible. One of these services is a searchable online portal.
Search the Medicinal Plant Names Services portal
Herbal medicines containing black cohosh are generally regarded as safe if taken as directed. Though poorly substantiated, some serious adverse reactions to black cohosh have been reported.
Extinction risk predictions for the world's flowering plants to support their conservation (2024). Bachman, S.P., Brown, M.J.M., Leão, T.C.C., Lughadha, E.N., Walker, B.E. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19592
