Eupatorium purpureum (Eutrochium purpureum (Linnaeus) E. E. Lamont), Kidney-root, Sweetscented Joe-Pie weed, Sweet Joe-Pye weed, or Trumpet weed is a herbaceous perennial plant native to eastern and central North America.
E. Purpureum is a clump forming plant that grows to 1.5 – 2.4 meters (5 – 8 feet) tall and about 1.2 meters (4 ft) wide. Plants are found in full sun to part shade in moisture retentive to wet soils. Stems are upright, thick, round, and purple, with whorls of leaves at each node. As the plant begins to bloom the stems often bend downward under the weight of the flowers. The leaves grow to 30 cm (12 in) long and have a somewhat wrinkled texture. The purpleish colored flowers are produced in large loose, convex shaped compound corymbiform arrays. Plants bloom mid to late summer and attract a lot of activity from insects that feed on the nector produced by the flowers. This species hybridizes readily with other species of Eutrochium and where this species and those species overlap in distribution the resulting plants can be difficult to resolve to a specific taxon. There are two varieties that differ in the pubescence of the stems and foliage, but many more have been proposed in the past, thought most authorities now accept that this is a variable species and population variations integrate.
E. purpureum is sometimes cultivated and has escaped from cultivation in parts of New Zealand.