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DescriptionThis perennial plant is 1-2½' tall and unbranched. The central stem is light green, 4-angled, and glabrous to short-pubescent. Pairs of opposite leaves are distributed rather abundantly along the central stem. Individual leaves are 1½-4" long and ½-1½" across; they are elliptic to broadly elliptic in shape and coarsely dentate along their margins. There is typically 5-7 large teeth along each side of a leaf. Each leaf tapers to a wedge-shaped base and it tapers gradually to an acute tip. The upper leaf surface is medium to dark green and hairless (or nearly so), while the lower surface is pale green and hairless to short-pubescent. Sometimes, the leaves become purplish green in bright sunlight. Dense whorled clusters of nearly sessile flowers occur above the axils of the middle to upper leaves. Each flower is about 1/8" (3 mm.) in length; it consists of light green calyx with 4-5 teeth, a white corolla with 4-5 tiny lobes, 2 slightly exerted stamens, and a pistil. The toothed calyx is 0.5-1 mm. in length; its teeth are broadly triangular. The corolla is 2.5-3.5 mm. in length; it is campanulate (bell-shaped). The blooming period occurs from mid-summer into the fall, lasting 2-3 months. Usually, only a few flowers are in bloom at the same time. Afterwards, each flower is replaced by 4 nutlets. The nutlets are 1.0-1.5 mm. long, obovoid, and 3-angled; the apex of each nutlet is tuberculate (bumpy) along the outer side, while the inner sides are flat and depressed. Taken together, the upper surface of each group of 4 nutlets forms an indented central area and a bumpy exterior. The root system is stoloniferous and tuberous. Vegetative colonies of plants are often formed.