Common tansy

Tansy is a flowering herbaceous plant with finely divided compound leaves and yellow, button-like flowers. It has a stout, somewhat reddish, erect stem, usually smooth, 50–150 cm (20–59 in) tall, and branching near the top. The leaves are alternate, 10–15 cm (3.9–5.9 in) long and are pinnately lobed, divided almost to the center into about seven pairs of segments, or lobes, which are again divided into smaller lobes having saw-toothed edges, giving the leaf a somewhat fernlike appearance. The roundish, flat-topped, button-like, yellow flower heads are produced in terminal clusters from mid-to-late summer. The scent is similar to that of camphor with hints of rosemary. The leaves and flowers are toxic if consumed in large quantities; the volatile oil contains toxic compounds including thujone, which can cause convulsions and liver and brain damage. Some insects, notably the tansy beetle Chrysolina graminis, have resistance to the toxins and subsist almost exclusively on the plant.