Common tansy, an escaped ornamental, is a perennial plant, from 1 ½ feet to 6 feet tall with showy button-like flowers. Originally imported from Europe as an ornamental, this member of the Sunflower family has now become widely established on the western slope of Colorado. Reproducing by both seed and rootstock, tansy is difficult to control. Tansy is particularly aggressive when growing along irrigation ditches where it can restrict water flow. It has been utilized as a medicinal herb and tea. Common tansy is sometimes mistaken for Tansy Ragwort, a poisonous plant. Alternatives to planting tansy include Yellow Yarrow (Achillea filipendula) and Woolly Cinquefoil ( Potentilla hippiana).