The balloon flower (Platycodon grandiflorum A. DC.) is a medicinal and perennial flowering plant. Jangback is an important white-flower type balloon flower cultivar registered in South Korea, but no molecular marker was available to differentiate it from other white-flower lines. Therefore, we evaluated five P. grandiflorum white-flower lines and identified a single nucleotide polymorphism (SNP) derived from the chloroplast TrnL-F genomic sequence that specifically differentiated Jangback from the other four genotypes. Cultivar identification was achieved by detecting allelic variations of the SNP using amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) analysis and high resolution melting (HRM) curve analysis. The present study describes a rapid and reliable method to authenticate the medicinally and economically valuable white-flower Jangback cultivar. Our results indicate that the plastid TrnL-F region provides for marker assisted identification and selection in intraspecific polymorphism studies, thereby the identified SNP marker provides a robust tool along with ARMS-PCR and HRM curve analysis for rapid and efficient identification of the medicinally valuable Jangback cultivar.