Many tiny yellow poppies are grown in the town area of Rishiri Island, Japan. Because the phenotype of this cultivated poppy is similar to that of Papaver fauriei, which is endemic to Mt. Rishiri, Rishiri Island, residents on the island call the cultivated poppy ''P. fauriei'' although the origin of the cultivated poppy is uncertain. To estimate the origin of the cultivated poppy, its internal transcribed spacer (ITS) sequence was compared with those found in the Far East wild poppies P. fauriei, P. alboroseum, P. miyabeanum and P. nudicaule. Although the ITS sequence of the cultivated poppy was not identical to those found in the wild species, it was most similar to that of P. miyabeanum, indicating that the cultivated poppy is not P. fauriei. However, cultivated poppy seeds have been sown several times over a period of at least 20 years in wild P. fauriei habitats on Mt. Rishiri in the hope of aiding the recovery of P. fauriei populations in wild habitats. Poppy plants in the wild habitats where such seeds have been sown showed the same ITS sequences as those of the cultivated poppy, indicating that the cultivated poppy is established in these wild habitats. This is a case of a nonindigenous species being introduced to wild habitats through human actions.