A foundation monograph of Ipomoea (Convolvulaceae) in the New World

Results
Molecular sequence data
Results from molecular sequencing and phylogenetic analysis have been of great value in our research at many levels (Wood et al. 2015; 2017a, b, d; 2018) and have enabled us to delimit Ipomoea as a genus, facilitating the study of its evolution (Muñoz-Rodríguez et al. 2018, 2019). It has enabled us to recognize major radiations in South America within Clade A1 (Figure 1) and in the Caribbean within Clade A2. It has confirmed the monophyly of some groups previously recognized on morphological grounds, such as Calonyction, Quamoclit, Astripomoea and Batatas (Muñoz-Rodríguez et al. 2019, supplementary data 3–8). Other accepted groupings, such as Argyreia, Pharbitis, Stictocardia and the Arborescens group are shown only to be monophyletic if certain species are excluded. Conversely, it has demonstrated that some recognized groups are not monophyletic (Turbina for example) and that Rivea is nested within Argyreia. Importantly the phylogenetic framework we have developed provides a context in which to interpret and understand the evolution of the many species of Ipomoea that lay outside the previously recognized segregate genera.
DNA sequencing and phylogenetic analysis has been valuable at the species level too. It has confirmed the monophyly of many species and has also drawn attention to the existence of unrecognized new species. We have many examples of this, such as the “discovery” of Ipomoea kraholandica in Brazil or I. lactifera in Bolivia, this last especially interesting as DNA confirmed it as belonging to the Batatas Clade and sister to the Old World species, Ipomoea littoralis. Sequence data has shown some species thought to be distinct are conspecific with others from different geographical areas, for example, I. acanthocarpa from Africa is the same species as I. piurensis from America, while I. lindenii from mainland America is the same as the Jamaican endemic I. cyanantha. In both these examples multiple specimens of the supposedly distinct species form a largely unresolved single clade confirming our morphological observations that the species are indistinguishable. DNA has also demonstrated that some species pairs thought to be possibly conspecific are indeed different; I. paludicola is distinct from I. asarifolia, I. marginisepala from I. cardiophylla and I. pterocaulis from I. jalapa. In these examples specimens from the two species do not form a clade separate from all other species. DNA has also shown that Ipomoea indica is not monophyletic and so consists of more than one entity, although we have not yet been able to unravel this complex. It has highlighted misidentifications when wrongly named specimens appear in parts of the tree separate from the clade where they belong. It has also provided a phylogenetic context to enable the interpretation of incomplete specimens, which lack diagnostic morphological information. However, molecular sequencing using ITS has severe limitations which are well documented, not least lack of resolution and support. For this reason, we have always used our ITS phylogeny in conjunction with hypotheses based on morphological characters. Nevertheless, we have been reassured that all major clades identified in our ITS tree are also inferred from the analysis of single-copy nuclear regions and of whole chloroplast genomes (Muñoz-Rodríguez et al. 2019).