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DescriptionThis perennial wildflower is 1-3' tall and usually unbranched. The erect central stem is light green (less often purplish green), 4-angled, and either glabrous or minutely pubescent. Pairs of opposite leaves about 2-4" long and ½-1½" wide occur at intervals along this stem. The leaves are lanceolate or elliptic in shape, and sparsely dentate along their margins (usually about 3-5 teeth on each side); some of the leaves may have margins with fewer or no teeth. Usually, the upper leaf surface is medium green and glabrous, while the lower surface is pale green and glabrous. Sometimes the leaf surfaces are minutely pubescent, particularly along their lower central veins. In bright sunlight, some of the leaves may acquire reddish coloration, particularly along their central veins. The leaves taper gradually to somewhat abruptly into petioles up to 1" long. Dense clusters of nearly sessile flowers occur along the middle to upper leaves; they are whorled around the central stem and located above the petioles of the leaves. Each flower consists of a light green calyx with 4-5 teeth, a white short-tubular corolla with 4-5 lobes, 2 slightly exerted stamens, and a pistil. The corolla is 3-5 mm long, while the calyx is 2-3 mm. long and its teeth are narrowly triangular. The blooming period occurs from mid-summer into the fall, lasting about 2-3 months. Usually, relatively few flowers are in bloom at the same time. Each flower is replaced by 4 nutlets about 1.0-1.5 mm. long; these nutlets are 3-angled and obovoid-oblong in shape; their upper surfaces are tuberculate (bumpy), particularly along their outer margins. The root system is rhizomatous or stoloniferous; it usually forms tubers. Small colonies of plants are often produced from the rhizomes or stolons.