Wood betony, also called common lousewort, often is found in large colonies. The flowers are in dense terminal clusters on unbranched stalks, light yellow, sometimes tinged with pink or purple, 2-lipped, the upper much longer than the lower, curving over the stamens. Each flower is subtended by an oblong, leaflike bract. Blooms April-May. Leaves are pinnately lobed, fernlike. Basal and most stem leaves are on long petioles; the stem leaves are alternate. At least the upper part of the plants is hairy. In early spring, the emerging leaves have a beautiful wine-red color.
Similar species: Swamp wood betony or swamp lousewort (P. lanceolata) flowers in summer and fall, grows in swampy open meadows and limey soils, and is most common in the southeastern Ozarks; its stem leaves are usually opposite, and the upper part of the stem is not hairy.