Eutrochium purpureum

Eutrochium purpureum is a clump-forming herb that grows to 1.5–2.4 meters (4.9–7.9 ft) tall and about 1.2 meters (3.9 feet) wide. Plants are found in full sun to part shade in mesic 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 purplish flowers are produced in large loose, convex shaped compound corymbiform arrays. Plants bloom mid to late summer and attract much activity from insects that feed on the nectar 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.[7] There are two varieties that differ in the pubescence of the stems and foliage, but many more have been proposed in the past, though most authorities now accept that this is a variable species and population variations integrate.

Many species of butterflies, moths, bees, and flies visit the flowers.[8]

It is larval host to the eupatorium borer moth (Carmenta bassiformis), the red groundling moth (Perigea xanthioides), the ruby tiger moth (Phragmatobia fuliginosa), and the three-lined flower moth (Schinia trifascia).[9]

The larvae of Calycomyza flavinotum, a leaf miner fly, create blotch-shaped mines on the leaves.[8]

Eutrochium purpureum is sometimes cultivated and has escaped from cultivation in parts of New Zealand.[10][11]