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DescriptionThis herbaceous perennial plant is 1½-4' tall and sparingly branched. Both basal and cauline leaves are produced that are similar in appearance. The central stem of each plant is light green (less often dark red), stout, terete, finely ribbed, and either glabrous or pubescent; the interior of this stem is hollow. Pairs of opposite leaves occur primarily along the lower one-half of each stem; they are widely spreading. These leaves are odd-pinnate with 4-9 pairs of sessile leaflets and a terminal leaflet (alternately, the leaves could be described as pinnatifid with 4-9 pairs of deep lobes and a terminal lobe); the leaves are up to 8" long. The leaflets are linear-lanceolate to lanceolate-oblong in shape with margins that are either smooth or sparingly dentate toward their tips. The upper leaflet surface is medium to dark green and glabrous, while the lower surface is more pale and either glabrous or slightly hairy. The rachis (central stalk) of each leaf is primarily white with winged margins that are green. The lower and basal leaves have longer petioles than the upper leaves; the latter are sometimes sessile. The central stem terminates in one or more flat-topped panicles of flowers about 2-5" across. On a robust plant, stalks of smaller flat-topped panicles may be produced from the axils of 1-2 pairs of upper leaves. The peduncles and pedicels of these panicles are light green (less often dark red) and either glabrous or pubescent. Individual trumpet-shaped flowers are about 4 mm. (3/16" ) long, consisting of a light pink or white corolla with 5 spreading lobes, a short green calyx with 5 teeth, 3 stamens, and a pistil with a style that is tripartite at its tip. The blooming period occurs during the summer for a month or two; the flowers are fragrant. Afterwards, the flowers are replaced by achenes with feathery hairs. The achenes are about 4 mm. (3/16") long, lanceoloid in shape, and slightly flattened; they are distributed by the wind. The root system is fibrous and rhizomatous. Colonies of clonal plants are sometimes produced by the rhizomes.