Common tansy is a perennial plant that reproduces by both seed and creeping rootstocks. Seeds are yellowish brown achenes with short, five-toothed crowns. Yellow flowers are numerous in flat-topped dense clusters at the tops of the plants. Button-like flower heads lack ray flowers. Flowering typically occurs from July to September. The leaves are alternate, deeply divided into numerous narrow, individual leaflets. Mature plants are 1.5 to 6 feet tall. Stems are often purplish-red in color and extensively branched towards the top. The foliage emits a strong odor when crushed.