An intraspecific chloroplast DNA (cpDNA) restriction site survey within Coreopsis grandiflora was used-to evaluate the correspondence of genetic variation with patterns of morphological differentiation and geographical separation. Eight frequent-cutting restriction enzymes were used with a sample of 273 individuals representing 14 populations from two geographical regions. Thirteen distinct cpDNA haplotypes were detected, differing by as many as 22 restriction site changes, or an estimated 0.674% nucleotide sequence divergence. The survey detected sufficient cpDNA variation for analyses of intraspecific and intrapopulational genetic structure and yielded evidence for interpopulational gene flow, a cpDNA polymorphism that transcends the species boundary, and possible cpDNA introgression. Patterns of genetic diversity do not strictly correspond to either morphological variation or geographical distribution; this may be a result of either cpDNA introgression or the maintenance of a cpDNA polymorphism through the speciation event that gave rise to C. grandiflora.