This southeastern species is locally common at least as far north as Mo., Tenn. and Va., but it is close to viridiflorum and there has been some confusion (F, Cr, W; Isely 1990). It has been reported from states north of Ky. in some databases (K, NS, PL), but sources need to be checked. For Ky. there are a few reported colls. from eastern margins of the Mississippian Embayment (Woods 1983, Chester 1992). The coll. from CALL could not be found at MUR, and at least one of the colls. from TRIG (APSC) was misidentified perplexum. However, another coll. from TRIG (APSC) does appear to be this species: W.H. Ellis #536, 14 Jul 1965, area around Hematite Lake. D. nuttallii is also known from ne. Tenn. and w. Va. in counties adjacent to Ky. A reported coll. from PIKE (NCU, F. Levy from railroad between upper bridge and cut-through) needs to be checked; and vegetative material that may be this species has been seen by JC in MCRE (near Natural Arch). D. nuttallii suggests transitions from viridiflorum to the paniculatum or ciliare group (Isely 1990). Based on Krings (2004) and other sources (as cited above), nuttallii can be distinguished from viridiflorum by its leaflets, which are narrower in shape (L/W mostly 1.5-2 versus 1-1.5), elliptic-ovate (versus rhombic-deltoid), and less densely villous. Also, loments (fruits) tend to be smaller, usually with 2-4 segments each 4-5 mm long (versus 4-5 of 5-8 mm). The loments usually have convex upper margins (versus straight). Mixed populations with several species often occur where ranges overlap, and variation among nuttallii-like plants does suggest intergradation at some sites.