Stems: slender, nearly simple. Leaves: ovate, acute, sinuate-toothed, sessile. Flowers: from the axils of the upper somewhat crowded leaves; corolla funnel-form, rarely expanding, the lobes deeply notched; calyx short and deeply cleft.

The pale lemon-coloured flowers of the Yellow Willow-herb grow in quantities near running water, or in the deep moist valleys where the rushes whisper in their husky throats and the moss weaves lace-like patterns to cover the ground. The plant stands from six inches to two feet high, and has large, conspicuously veined leaves, with wavy margins, which are very sharply toothed. The flowers are extremely pretty and delicate in hue; their four petals, folded in funnel-form, rarely expand, and are held up in green calyx-cups, which in their turn are cleft into four narrow slender divisions.