Hybridization between native and exotic dandelions (Taraxacum japonicum and T. officinale), and their expansion have been reported in Japan. To declare the expansion process of hybrids would contribute to understanding how the hybrids have expanded and predicting how they will affect the original species. Present study examined population genetic structure for the native, exotic and hybrid dandelions at some sites.

Leaves and head flowers of dandelions were collected in some parks in Osaka. The samples were classified into native, exotic, and 3n and 4n hybrids, from the form of involucre, the fragment length of nuclear DNA at ITS region, and the relative amount of DNAs. DNA was extracted from the leaf samples, and genotypes were determined by using 6 SSR markers. 10 maturing fruits were tested whether it is native or hybrid for each native sample.

Few clones were found in hybrids. In addition, a hybrid fruit was found in 1891 fruits from 192 individual. These indicate that the hybridization is not rare phenomenon. Within site, genetic distance between natives and hybrids were larger than that between natives and exotics, indicating that the hybrids were not formed within the study site.

These results indicate that the hybrids have been frequently formed, however most of them distributed in the sites were imported from the other site.