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Any of certain plant species of the genus Tanacetum native to South Asia, whose aromatic flower heads, when powdered, constitute the active ingredient in the insecticide pyrethrin (or pyrethrum). The concentrations of pyrethrum powder used in insecticides are nontoxic to plants and higher animals; these insecticides therefore find wide use in household and livestock sprays as well as in dusts for edible plants. The typical species, the perennial T. coccineum, also is the florists' pyrethrum, or painted lady. Large petals of a deep rose colour surrounding the yellow centre, or disk, are borne on long, simple stems above the crown of finely cut leaves.
This entry comes from Encyclopædia Britannica Concise. For the full entry on pyrethrum, visit Britannica.com.