The ornamental plant Hydrangea macrophylla has various inflorescence types, including its wild forma. The mophead inflorescence, which is considered to be a cultivated type, is particularly distinctive compared with the wildtype（lacecap）inflorescence. However, plants with mophead inflorescences grow with the wildtype along the Jogasaki coast on the Izu Peninsula, Shizuoka Prefecture, Japan, indicating that this inflorescence type may be a natural form. To test the hypothesis, we conducted genetic analysis of wild individuals from the Jogasaki coast, along with examples from Irozaki on the Izu Peninsula and Kozu Island, based on single nucleotide polymorphisms（SNPs）obtained by MIG-seq. Based on 281 SNPs, we were able to distinguish individuals from the populations on Kozu Island and the Izu Peninsula, and slightly distinguish those from populations of Jogasaki and Irozaki in the Izu Peninsula. Expected heterozygosity did not differ between the two types of inflorescence from Jogasaki. Furthermore, geographic distribution and genetic similarity exhibited weak spatial autocorrelation in Jogasaki. This evidence suggests that mophead inflorescences appear naturally in Jogasaki. This is an important genetic resource that should be conserved.