Amaranthus tortuosus, Hornem.

Hassan, Walaa A., Al-Shaye, Najla A. & Iamonico, Duilio, 2023, A critical inventory of the family Amaranthaceae s. str. in Saudi Arabia, Phytotaxa 626 (4), pp. 223-246 : 240

Amaranthus tortuosus

POWO (2023) reports Amaranthus tortuosus Hornem. as an alien species in Saudi Arabia, but no relevant literature source is listed. Note that neither Chaudhary (1998) in the most recently published Flora of the Kingdom of the Saudi Arabia, nor Thomas (2011 +) in the continuously updated Checklist of the Flora of Saudi Arabia, and Hassan et al. (2022) in their taxonomic revision of Arabian amaranths, listed this species among the Amaranthus taxa occurring in the country. We did not trace any work, referring to Saudi Arabia, in which A. tortuosus was reported, and did not find this species in field.

Hornemann (1819: 107) published Amaranthus tortuosus from plants cultivated in Hortus regius botanicus Hafniensis (what is now the Botanical Garden of Copenhagen) from seed collected in Saint Croix Island ( Virgin Islands, U.S.A.) as reported in the protologue (“ Hab. in Ins. St. Cru. [Habitat in Insulis Sanctus Crucis] ... C. intr. [Planta Caldari introducta] 1816”; see Hornemann 1819: IX). In fact, according to POWO (2023), A. tortuosus is a species native to Mexico, Central America, the Caribbean, and north-western tropical regions of South America. Among the listed synonyms in POWO (2023), there is A. dubius Mart. ex Thell. , a species accepted by many authors as distinct (e.g., Mosyakin & Robertson 2003, Iamonico 2015b, Sindhu et al. 2021b, Hassan et al. 2022) and recently discovered in Saudi Arabia ( Hassan et al. 2022: 149–150). However, based on a preliminary check of the protologue of A. tortuosus ( Hornemann 1819: 107) as well as the examination of original material by one of us (DI), A. tortuosus cannot be ascribed to A. dubius but likely to A. hybridus . Note also that, among the synonyms of A. tortuosus listed in POWO (2023), there are two varieties of A. tristis L., viz. var. xanthostachys Moq. (= A. dubius according to Iamonico 2016c: 104–105) and A. tristis L. var. flexuosus Moq. (possibly A. dubius according to Iamonico 2016c: 103–104). A complete study of Hernemann’s name is in preparation by DI.

All details considered, we exclude Amaranthus tortuosus from the flora of Saudi Arabia .