Pyrethrum, the name of several kinds of perennial herbs that were formerly grouped in their own genus but are now classified as chrysanthemums. Pyrethrum is also the name of an insecticide made from the dried blossoms of these plants. One species, native to the Caucasus region of Europe, is widely grown in the United States for its showy, daisylike flowers. This plant is also known as painted daisy and painted lady.

This species and (more commonly) a species native to Croatia are cultivated commercially in California, Ecuador, Peru, Japan, and parts of Europe and Africa for making the insecticide. Pyrethrum dust or spray kills mosquitoes, flies, lice, fleas, bedbugs, and several crop-destroying insects. It is less harmful to human beings than are most other insecticides. Pyrethrin is a synthetic insecticide identical to one of the toxic agents in pyrethrum.

The pyrethrum from the Caucasus is Chrysanthemum coccineaum. (In seed catalogs it usually is called Pyrethrum roseum.) The species from Croatia is C. cinerariaefolium. Both belong to the composite family, Compositae.