This polyploid is widespread in northeastern wetlands; 2n = 56, 84 and 112 (FNA 8). It extends south to s. Ill., s. Ind. and s. Ohio (K). It was collected by C.W. Short (PH) ca. 1830: "muddy thicket, Henderson Co., Ky., near Mr. William Greers, fl. 10th May. The only place I have seen it." There is a closely related mid-western taxon known as M. forbesii (Vasey) Bush, which is distinguished as follows (W): leaves pilose on the lower surface (versus glabrous or sparsely pubescent)); petals longer than sepals (versus about as long). M. forbesii is largely restricted to seepage zones below sandstone cliffs from Mo. and s. Ill. to Minn. and Wis., and has been reported from Ky. (W), but perhaps based on erroneous interpretation of the Short coll. Further checking is needed at PH.;