Africa and Arabia encompass a much greater species diversity in the Achyranthes aspera aggregate (Amaranthaceae, achyranthoid clade): Evidence from morphological and chorological data

Abstract

Achyranthes in its traditional sense (excluding Achyropsis that phylogenetically falls into Achyranthes) has been considered to contain a restricted (three to four) number of species in Africa and one or two species in the Arabian Peninsula. The morphology of the type species of the genus, A. aspera, has been treated as highly polymorphic, with several varieties recognised by various authors. Not surprisingly, a recent extended phylogeny revealed a non-monophyly of A. aspera. We present a deeper insight into morphological characters of the A. aspera aggregate together with taxonomic, nomenclatural, ecological, and chorological data based on field investigations and herbarium studies. Instead of one polymorphic species, we accept A. aspera s.str., A. abyssinica, A. acuminata, A. annua, A. mauritiana, A. porphyrostachya, A. sicula, and A. seychellensis sp. nov., all being native to different parts of Africa. In most herbaria, the vast majority of African specimens labelled as A. aspera belong to other species, which are being reinstated here. In addition, two well-recognized species, A. fasciculata and A. talbotii from Tropical East and West Africa, respectively, are also discussed. Moreover, we found that the type of A. aspera var. pubescens as listed in the African and Arabian floras and checklists belongs in fact to an American species A. fruticosa, which is absent in the Old World. In place of the misapplied A. aspera var. pubescens, we accept A. porphyrostachya, a species described from Myanmar, as a correct name for the populations growing in Africa and Arabia. According to our results, at least 10 native species of Achyranthes occur in Africa (or 16 species if Achyropsis is merged with Achyranthes), which is a major diversity center of the genus. Four species are recorded from the Arabian Peninsula (A. abyssinica, A. annua, A. aspera s.str., A. porphyrostachya), and two of them (A. abyssinica and A. annua) reach their easternmost range limit in this region. As a result, the distribution as well as ecological conditions of each species is now clarified or circumscribed for the first time.