This is a widespread eastern annual or short-lived perennial on damp, acid soils, especially in disturbed areas. Further review of colls. is desirable in order to assess variation within mutilum and to check for the presence of two related species: the southeastern H. gymnanthum Engelm. & Gray, and the northeastern H. boreale (Britt.) E. Bickn. Both of these species are known in Ill., Ind. and Ohio (K). Also, hybrids can be expected among these species and with canadense; 2n = 16 in all cases (Cr, F, W).