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A genus of about twenty species in N. America, Mexico, and N.E. Asia, allied to Neillia, in which it was included in previous editions of this work. It differs in its valvate calyx-lobes (imbricate in Neillia) and in having inflated follicles that open down both sides. Also the inflorescence is usually corymbose (racemose or paniculate in Neillia). They need a moist soil and should be grown in full sun.