Abstract:The flower of the new genus Tetradoxa (Adoxaceae) has been studied in detail. Its flower is almost 4merous. On rare occasions it is 3- merous or 5-merous. Their numerical ratio of calyx- and corolla-- lobes is always equal to one. The variations of the flower parts are not frequency like Adoxa. It is no doubt that the outer lobes are calyxes and the inner lober are corollas. The bundle fusion in the vasculariation of the flower in Tetradoxa is less than that in Adoxa. In our opinion, Tetradoxa is stayed on a original: position in the infrafamiliar evolution.