Pyrethrum was a genus of several Old World plants now classified as
Chrysanthemum or
Tanacetum (e.g.,
C. coccineum) which are cultivated as ornamentals for their showy
flower heads.
Pyrethrum continues to be used as a common name for plants formerly included in the genus
Pyrethrum. Pyrethrum is also the name of a natural
insecticide made from the dried flower heads of
Chrysanthemum cinerariifolium and
Chrysanthemum coccineum.