This perennial wildflower is usually an emergent aquatic that is exerted 1-3' above the water line, otherwise it is a terrestrial plant of similar height. The stems are usually unbranched, although larger plants are sometimes branched below. The stems are light green, angular-terete, and glabrous. At intervals along each stem, there are pairs of opposite leaves about 2-6" long and ¼-1" across that are either sessile or short-petioled. The deciduous leaves are narrowly lanceolate, linear-lanceolate, elliptic, or narrowly elliptic in shape and usually smooth along their margins. Less often, the outer margins may be slightly undulate or shallowly crenate. Both the upper and lower surfaces of the leaves are medium green and glabrous. From the axils of the middle to upper leaves, there develops individual spikes of flowers on long peduncles. Each floral spike is about 1" long and capitate (head-like) in appearance; there are several overlapping flowers and buds per spike. Each flower is about ¾" across, consisting of a short-tubular corolla with 4 lobes, a short-tubular calyx with 5 teeth, 2 stamens with dark purple or dark brown anthers, and an ovary with a slender white style. The corolla has a shallowly notched upper lobe that curves backward, 2 lateral lobes that are widely spreading, and a lower lobe that curves slightly downward. Except for the dark purple mottling at the base of the lower lobe, the lobes are mostly white, otherwise they are tinted pale purple or they are lightly speckled with fine purple dots. The lobes of the corolla are longer than the corolla tube, and they are oblong to oblong-oblanceolate in shape. The green calyx is about ¼" long and glabrous; its teeth are narrowly lanceolate. The ascending straight peduncles are a little shorter to about as long as the leaves (up to 6" in length); they are medium green, angular, and glabrous. The blooming period occurs from early summer into the fall, lasting about 2-4 months. Usually, only a few flowers are in bloom at the same time. Afterwards, the flowers are replaced by seed capsules up to ½" long that taper to stipe-like bases. Each capsule has 2 cells, and each cell contains 2 seeds. The seeds are about 1/8" (3 mm.) in length and warty. The root system is highly rhizomatous, forming colonies of plants.