Evolution of morphological traits of Dendrobium sensu lato (Orchidaceae)—an attempt to resolve phylogenetic relationships in nominal and morphologically convergent sections

Abstract Background Dendrobium is a large genus within the Orchidaceae family, containing over 1,600 species. Most are sympodial epiphytes. These species are distributed throughout southern, eastern, and southeastern Asia, the Pacific Islands, Australia, New Guinea, and New Zealand. Infrageneric classification of this group is challenging, largely because of the large number of taxa, the wide geographic range, and the considerable morphological diversity. The primary objective of our research was to analyze the genus Dendrobium (focusing primarily on the nominal section) using DNA sequences and to integrate these findings with morphological data. Results UPGMA morphological analysis and SIMPER analysis, considering 14 characters, showed that characters such as the placement of the inflorescence, the pseudobulbs from which the inflorescence grows, the surface of the lip, and the number of lobes on the lip are the distinguishing characters of the taxa within Dendrobium sensu lato.The nominal section, Stachyobium, and Formosae (species-rich) are more morphologically variable and exhibit a wide range of variability, in contrast to sections with fewer species. The reconstruction of the ancestral states of Dendrobium sensu lato showed that most of the characters examined arose independently several times during evolution. The only exception is dorsiventrally compressed leaves, a character that arose only once. In addition, the nominal section is not monophyletic and is not entirely consistent with morphology, and species of Holochrysa, Breviflores and Stuposa are closely related. Conclusion We conclude that convergent evolution likely occurred among Dendrobium sensu lato representatives, and that many floral traits may have resulted from adaptations to pollinators. This has led to numerous classification problems within the genus. We have not received a clear answer to the question of how to classify species across the genus. Therefore, in this study, we focused primarily on the nominal section.