Amaranthus powellii S. Watson and A. bouchonii Thell., two newly naturalized species in China.
About twenty Amaranthus species have been recorded in China and most are alien weeds. The morphological characteristics are similar under genus, and often occurrring misidentifications. We found two newly alien species from submitted specimens which were identified as another species. Two Chinese epithets were entitled separately by the Latin names of specific meaning. Amaranthus powellii S. Watson and A. bouchonii Thell., two invasive plants from Southwest USA and Europe separately, are similar on morphology, monoecism, pistillate flowers with 3-5 unequal tepals, equal or short of utricle, utricle dehiscence or indehiscence. Both of them can be distinguished by numbers and shapes of tepals, features of utricles, and shapes and sizes of bracts. In this paper, their Chinese description, color illustrations, key features and distribution and harmful status are provided as well.