A long-lived herbaceous plant or small shrub usually growing 0.5-2 m tall. Its reddish or purplish stems are finely hairy when young, but become hairless as they mature. Its paired leaves (1-10 cm long and 0.7-5 cm wide) are usually purple-tinged or bright reddish-purple in colour. Its tiny whitish flowers are arranged in dense clusters (7-20 mm long) in the upper leaf forks or at the tips of the branches. These clusters are rounded to slightly elongated in shape and are borne on stalks usually 3-10 cm long. Its tiny brown fruit (1.5-2 mm long) contains a single seed and usually remains hidden within the old flower parts.