A plant of European origin, it is an erect, hairy perennial that can reach up to 2m high. It has 30-50 stems and forms wide-topped crowns. The stems are reddish-purple or red to purple and square in cross-section and the downy leaves are lance-shaped. Showy spikes of rose-purple flowers appear in summer. The flowers are10-20mm in diameter, with six petals (occasionally five) and 12 stamens, clustered tightly in the axils of bracts or leaves. The fruit is a small 3-4mm capsule containing numerous minute seeds.