A tale of many twists and turns: multidisciplinary taxonomic analysis sheds light on the long-disputed identity of Galianthe laxa subspecies (Spermacoceae-Rubiaceae)

Abstract The taxonomic delimitation of Galianthe laxa subspecies has long been disputed and remains unclear. Galianthe laxa subsp. laxa is widely distributed throughout South America, whereas G. laxa subsp. paraguariensis is endemic to Paraguay and has never been included in molecular phylogenetic analyses. Morphologically, they have been differentiated by leaf, habit, and inflorescence characteristics. Taxonomically, they were described as species and subsequently underwent repeated reclassifications. This prompts the question of whether they should be recognized as subspecies or as species. Therefore, a comprehensive approach was applied, combining macro- and micromorphological (including scanning electron microscopy pollen images), morphometric, chorological, and molecular data (new sequences were obtained for G. laxa subsp. paraguariensis). The sample comprised 196 specimens, of which 50 were selected for morphometric analysis. This compelling evidence provided robust support to revalidate Galianthe paraguariensis as a distinct species. By untangling this contentious infraspecific problem and clarifying species delimitation, this study illustrates how the combination of multiple lines of evidence in integrative taxonomy can also provide identifiable targets on which conservation efforts can be focused and can contribute to a better understanding of evolutionary relationships in a broader context, in this case within the Neotropical Spermacoceae tribe.