[Objective] This study aimed to analyze the ploidy of Chinese old roses and their progenies. [Method] The ploidy level of 38 roses was examined by the flow cytometry. [Result] The four Chinese old roses that influenced breeding of mod- ern roses were diploid. Since the progenies of these Chinese old roses crossed with the tetraploid European old roses were almost tetraploid, it is probable that the pro- genies were arisen by the unreduced gametes of the Chinese old roses. Other Chi- nese old roses analysed were triploid, it was presumed that triploids and diploids were intermingled in China of the 1700s and the plant hunters preferred the more fertile Chinese old roses to be introduced to Europe. Sixteen hybrids of Chinese old rose originated in China consisted of six diploids, five triploids and five tetraploids. [Conclusion] Although these diploid Chinese roses might be the progeny brought by crossing among only Chinese old roses, it was considered that triploids and tetraploids have been arisen by crossing between European old roses and Chinese old rose.
