Leaflets: blade apex acute to obtuse. Inflorescence bracts lanceolate to ovate. Petals white, (7-)8-13(-16) mm. Stamens (6-)12-28(-40) mm, longest ones ca. 2 or more times as long as petals. Seeds roughened. 2n = 20. Flowering summer-early fall. Gravelly or sandy, sunny places along streams, sandy places, open woodlands, grasslands, roadsides; 100-1500(-2100) m; Alta., Man., Ont., Sask.; Ala., Ariz., Ark., Calif., Colo., Conn., Idaho, Ill., Iowa, Kans., Ky., La., Md., Mass., Mich., Minn., Mo., Nebr., Nev., N.Mex., N.Dak., Ohio, Okla., Pa., S.Dak., Tex., Utah, Va., Wash., W.Va., Wyo.; Mexico. Subspecies trachysperma is found mainly in the Great Plains and western states. Populations in the eastern United States are presumably adventive, as are those in eastern Ontario, where it has been found spreading in disturbed areas, such as quarries and roadsides (B. McBride 2006).