They are herbaceous, mostly perennial plants (some annual or biennial) growing to 0.5-3 m tall, with simple or branched stems. The leaves are spirally arranged, entire to deeply lobed, 5-25 cm long. The flowers are produced in daisy-like inflorescences, with yellow or orange florets arranged in a prominent, cone-shaped head; "cone-shaped" because the ray florets tend to point out and down (are decumbent) as the flower head opens.
A large number of species have been proposed within Rudbeckia, but most are now regarded as synonyms of the limited list given below. Several of these currently accepted species have several accepted varieties. Some of them (for example the Black-eyed Susan, R. hirta), are popular garden flowers, distinguished for their long flowering times. There are many cultivars of these species.
The name was given by Carolus Linneaus in honor of his teacher at Uppsala University, Professor Olof Rudbeck the Younger (1660-1740), and his father, Professor Olof Rudbeck the Elder (1630-1702), both of whom were botanists.Species