Revision of Alternanthera (Amaranthaceae–Gomphreneae) in the Arabian Peninsula, with nomenclatural corrections and notes on A. pungens and A. sessilis in the Old World

Background and aims – Alternanthera is one of the largest genera in Amaranthaceae, with the primary distribution in the Americas. The identification of some species, including those occurring as alien noxious weeds in the Old World, is challenging because of unstable taxonomy and nomenclature. In addition, their means and history of introduction remain poorly understood. Here, we revise the alien species of Alternanthera in the Arabian Peninsula, providing notes on their morphology, distribution, nomenclature, and dispersal facilities. Material and methods – We analysed type specimens, vegetative, floral and fruit characters, introduction history, and occurrences of four species of the genus in the Arabian Peninsula. Key results – Alternanthera ficoidea is reported for the first time from the Arabian Peninsula, and A. sessilis is newly recorded in the United Arab Emirates. The history and means of the species introduction are discussed. The turbulent nomenclatural history of A. ficoidea and A. tenella is reviewed to resolve the current confusion in their European records, and we propose that the latter name should unambiguously be considered as a synonym of A. ficoidea . The original spelling of Telanthera “ bettzickiana ” and A. “ bettzickiana ” are researched, and the species epithet is corrected to “ bettzichiana ”. A lectotype is designated for A. achyranthes , the generic type of Alternanthera . Detailed morphological descriptions of the propagules of Alternanthera are provided, and their role in the dispersal process are discussed. Conclusion – We noted a recent expansion of Alternanthera ficoidea , A. pungens , and A. sessilis in natural and anthropogenically disturbed plant communities of the Arabian Peninsula, especially across the coastlines of the Arabian Sea and Red Sea, and in foothills of the Sarawat Mountains. Their spread occurs through both vegetative and sexual means of dispersal. Our examination of morphological characters reveals a distinct role of the perianth and pericarp in the propagule dispersal of these species.