There are about 6 species in Rehmannia, of which, Chinese traditional medicine R. glutinosa distributed from East Asia to Japan, all others are endemic to China. As worldwide studies emphasized on R. glutinosa but neglected other species, it leaves us many unsettled problems related to Rehmannia, such as, how to differentiate R. glutinosa from similar species, where is R. elata, and how about the phylogenetic development of the genus. This thesis is an exploration aimed to all those problems from the view o...