Atrema DC. is a small genus of annual flowering herbs in the carrot family (Apiaceae), order Apiales. The genus was described by Augustin Pyramus de Candolle, published in Collectanea Memoires (1829) and Prodromus (1830). It contains a single accepted species, Atrema americanum Nutt. ex DC., commonly known as prairie bishop or prairie bishop's weed.
Plants are slender annuals with leaves that are doubly pinnatisect (cut into fine segments). The inflorescence bears both bracts and bracteoles. Sepals are absent; petals are white, slightly notched at the tip (emarginate) with the tips inflexed. Fruits are schizocarps composed of two mericarps that are nearly spherical (subglobose) with distinctly warty (rugose) exteriors; the stylopodium is short; ribs are insignificant in cross-section; vittae (oil canals) are not apparent; seed endosperm is concave.
Atrema americanum is native to the south-central United States, with confirmed occurrences in Texas, Arkansas, Oklahoma, and Alabama. It grows in prairie and grassland habitats and is sometimes encountered in disturbed areas within its range.
In some botanical treatments Atrema americanum is placed as a synonym of Bifora americana (A. Gray) within the genus Bifora, which is circumscribed more broadly to include one American and two Eurasian species. Under that circumscription, Atrema is subsumed into Bifora (tribe Coriandreae). The GBIF backbone recognises Atrema DC. as an accepted genus distinct from Bifora.
Distribution
Atrema americanum (prairie bishop) is native to the south-central United States, with native occurrences documented in Texas, Arkansas, and Oklahoma; it has also been introduced in Alabama. GBIF occurrence records confirm concentrations in Texas.
Taxonomy Notes
Atrema DC. (1829–1830) is variously treated as an accepted monotypic genus or as a synonym of Bifora Hoffm. (1816). The GBIF backbone recognises Atrema DC. as accepted with one species, Atrema americanum Nutt. ex DC. Other sources place this plant as Bifora americana within the broader genus Bifora (tribe Coriandreae, family Apiaceae). The Wikipedia article on Bifora redirects from “Atrema,” reflecting this synonymy.
