Any of the ornamental plants that make up the genus Chrysanthemum , in the composite family .
The genus includes about 100 species native primarily to subtropical and temperate areas of the Old World. Cultivated species, often called mums, have large flower heads; those of wild species are much smaller. Most species have aromatic, alternate leaves. Some have both disk and ray flowers in the heads; others lack ray flowers. Costmary ( C. balsamita ), pyrethrum , marguerite , Shasta daisy (hybrid forms of C. maximum ), florists' chrysanthemum ( C. morifolium ), feverfew ( C. parthenium ), corn marigold ( C. segetum ), and tansy are popular garden plants. Feverfew and pyrethrum are used in insecticides; feverfew and tansy were formerly used in medicines.