Dahlia pinnata is a species in the genus Dahlia, family Asteraceae, with the common name garden dahlia. It is the type species of the genus and is widely cultivated.
Dahlia pinnata is a perennial herbaceous plant with a rhizome and tuberous roots, reaching a height of 70 to 120, rarely 160 centimeters. The stem is erect being branched only in the inflorescence. The leaves are usually simple, with leaflets that are ovate and 5–10 cm long. The plant is slightly shaggy. The two to eight flower heads have a diameter of 6 to 10 centimeters on 5 to 15 centimeters long stems. The eight florets have a length of 3 to 5 centimeters, are ovate and coloured pink to deep purple. The flowering period extends from July to October.