Aquatic and Wetland Vascular Plants of the Northern Great Plains
Eupatorium L.
Stout, erect perennials from a thick rootstock; leaves simple, opposite
and connate-perfoliate or whorled and short-petiolate, serrate. Heads
discoid, usually numerous and clustered in a terminal corymbiform inflorescence;
involucral bracts in 2-4 series, imbricate or weakly so, green or colored
like the corollas; receptacle flat to conic, naked; disk florets
perfect, their corollas pinkish-purple to purple or white; style branches terete,
elongate, papillose. Achenes 5-angled, glandular; pappus of numerous
capillary bristles.