Three to five feet high. Stem. - Densely hairy, stout, branching. Leaves. - Mostly opposite, lance-oblong, finely toothed. Flower. - Purplish, pink, small, in the axils of the upper leaves, or in a leafy, short raceme. Calyx. - Four or five-parted. Corolla. - Of four petals. Stamens. - Eight. Pistil. - One, with a four-parted stigma.

The hairy willow-herb is found in waste places, blossoming in midsummer. It is an emigrant from Europe.