How many different breeds of hamster are there?

There are 23 species of hamster, with five commonly kept as pets: the Syrian hamster (Mesocricetus auratus), the Chinese hamster (Cricetulus griseus), the Roborovksi dwarf hamster (Phodopus roborovskii), the Campbell's dwarf hamster (Phodopus campbelli), and the winter white dwarf hamster (Phodopus sungorus).