In its broad traditional sense, this species is widespread across eastern North America but largely restricted to seasonally wet acid soils. It is reportedly a "facultatively agamospermic polyploid [2n = 45, 60] compilospecies in which unidirectional gene flow from related diploids [including magnicamporum, odorata and ochroleuca] generates a wide range of novel forms and races" (C.J. Sheviak & P.M. Brown in FNA 26); other species of Spiranthes in Ky. are mostly diploid (2n = 30). There appear to be at least three segregates with distinct key characters and DNA sequences (FNA 26, Dueck et al. 2014, Pace & Cameron 2017). A widespread segregate occurs mostly in the Mid-west and Great Lakes regions, mostly north of the glacial limit; and has recently been recognized as a species: S. incurva (Jenn.) M.C. Pace. In its strict sense, cernua is now considered a largely southeastern species that overlaps little in range with incurva (Pace & Cameron 2017). S. incurva is close to typical cernua but appears to have originated from hybridization with magnicamporum. It has not been reported from Ky. but it is expected. S. incurva reportedly differs from cernua s.s. as follows: labellum centrally yellowish, at least faintly (versus essentially white); lateral sepals linear-lanceolate (versus lanceolate); flowers frequently ascending (versus frequently nodding); occasionally with peloric or cleistogamous flowers (versus rarely so). Another segregate is the newly described S. arcisepala M.C. Pace, which occurs mostly at higher elevation in the Appalachians to New England and may be expected in the Cumberland Mts. S. arcisepala reportedly differs from ochroleuca, cernua, incurva as follows: lateral sepals downwardly falcate (versus sweeping upward), apices pointing toward the labellum apex (versus toward dorsal sepal and petals). It is also notable that colls. from BELL (KY) and elsewhere in southeastern counties are relatively robust and somewhat similar to odorata. Records of Ettman & McAdoo (1979) were based on herbarium colls. but need to be confirmed; they include a cluster in the Bluegrass region, where odorata has also been found.