Any of three genera ( Echinacea , Ratibida , and Rudbeckia ).
They are weedy plants in the composite family, native to North America. Some species in each genus have reflexed ray flowers. The purple-flowered perennials E. angustifolia and E. purpurea are often cultivated as border plants; they have strong-smelling black roots and hairy stems. These two species, along with E. pallida , are used to prepare an herbal cold and flu remedy called echinacea. Ratibida species have yellow ray flowers and brownish disk flowers. Prairie coneflowers ( Ratibida columnaris and R. pinnata ) are grown in wildflower gardens. Rudbeckia species have yellow ray flowers and brown or black disk flowers. Black-eyed Susan ( Rudbeckia hirta ), thimble-flower ( R. bicolor ), and cutleaf coneflower ( R. laciniata ) are grown as border plants.