Its four-angled stem is glabrous to pubescent.
Margins are entire.
Leaf surfaces are pubescent. Calyx lobes number six. They differ from purple loosestrife by having solitary or paired flowers in the leaf axils, rather than many flowers in terminal spikes, and six to eight stamens rather than twelve. Purple loosestrife is a highly aggressive, perennial wetland plant native to Eurasia. It was introduced to the northeast coast of North America in the early 1800's as a contaminant of European ship ballast and as a medicinal herb.