This annual is widespread across eastern and central states, but it may have spread east from an original range centered in Tex., Okl. and Ark., as reviewed by Ward (2006). The first colls. from Ky. were made in the 1820s under the name V. tenella Raf. ex Muhl. (Merrill 1949); see also, Short & Peter (1834). However, the only known pre-1900 coll. with locality data was made by C.W. Short (PH, MICH) in 1836 at "Blue Licks, poor hills" (ROBE;); Pr did not list it but see notes under arvensis The earliest records from Ohio and Tenn. date from the 1890s (Gattinger 1901; SERNEC). Most recent treatments have maintained rafinesquei as a distinct species (Cr; McKinney & Russell 2002; W). However, it is closely related to the southern European V. kitaibeliana Schult. and has been combined as a variety by other authors (e.g. F; Ward 2006). Chromosome numbers in this weedy complex range from 2n = 14 or 16 to 48 (Yockteng et al. 2003), but morphological and biogeographic differences are not well documented. Flowers are usually pale blue; plants with deeper blue flowers may deserve more attention, and colls. should be reeaxmined for potential segregation. See also notes under arvensis.