One species with a disjunct distribution or two with convergentevolution? taxonomy of two South American garlics

Abstract

The establishment of species boundaries has been a difficult task for biologists since the beginning of classifications. Within South American Allioideae (= Alliaceae), the delimitation of genera and species has long been a major challenge. Consequently, species-level nomenclature in these groups has been difficult to elucidate. Ipheion and Tristagma are two closely related South American genera for which the delimitation and circumscription of several species continue to be unclear. Tristagma sessile, a species inhabiting the Andes and the Coast Range in Chile, and Ipheion recurvifolium, a species native to Uruguay only found close to sea level, have been considered as one species with an intracontinental disjunct distribution. The divergent habitats and distributions of these taxa have stirred the question of whether they are a single species. The present study aims to elucidate the evolutionary relationships and status of the Chilean and Pampean taxa. We also analysed the name Tristagma leichtlinii, which has long been a source of confusion. Based on their phylogenetic relationships, geographical distributions, flowering periods, and DNA content, we conclude that the two taxa are different species and assignable to separate genera. We propose that the morphological similarity of Ipheion recurvifolium and Tristagma sessile, amply corroborated in this study, might be the sum of shared synapomorphies (between Ipheion and Tristagma) and convergent features. We update the biogeographic history of the two genera and propose that similar pollinators might underpin the convergence in floral traits. We outline the differences among genera and species, present a taxonomic review with a new lectotype and consider the conservation status of the studied species.