There are several different types of siamensis plants and two in particular have become popular in aquaria since their introduction decades ago. Known then as C. blassii and C. siamensis these are now considered to be just different morphotypes of C. cordata siamensis. But, they're distinct plants, one 'type' is considerably larger than the other and has narrower leaves. Rosanervig corresponds to the siamensis type - there is no pink veined plant that looks like blassii.
Oriental Plants Co. In Asia is one of the handful of nursuries that supply most of the pet trade. This is the plant they've been selling as C. cordata 'Blassii'.
