Nomenclature survey of the genus Amaranthus (Amaranthaceae): 12 questions about Amaranthus caudatus

Nomenclatural and taxonomic issues concerning Amaranthus caudatus and the related taxa are presented. Types are designated for names A. caudatus var. albiflorus (neotype at RO), A. caudatus var. atropurpureus (neotype at GH), A. caudatus var. gibbosus (neotype at RO), A. dussi (neotype at NAP), and A. edulis (lectotype at LP). Holotypes are indicated for the names A. caudatus var. pseudopaniculatus f. oblongipetalus (EA), A. caudatus var. pseudopaniculatus f. pseudopaniculatus (EA), A. caudatus subsp. saueri (PR), and Amaranthus edulis var. spadiceus (CORD). The names A. caudatus var. albiflorus, A. caudatus var. atropurpureus, A. caudatus subsp. saueri, A. dussi, and Amaranthus edulis var. spadiceus are considered as hererotypic synonyms of A. caudatus. On the basis of morphological, cytological, and molecular data, the taxa caudatus, mantegazzianus, and gibbosus are here proposed to be treated as different species. A new name—Amaranthus baileyanus—is proposed for A. caudatus var. gibbosus because of a previous and validly published Amaranthus gibbosus.