Characterizing North American Ipomoea grandifolia (Convolvulaceae), a member of Ipomoea series batatas

Species in the genus Ipomoea are often difficult to identify due to their similar morphologies and their ability to hybridize with one another. An undescribed North American Ipomoea morphotype in series Batatas, referred here as Ipomoea Carolina morphotype, was found to be morphologically, genetically, and reproductively isolated from other locally co-occurring Ipomoea species. A previous phylogenetic analysis that included a broader sampling of species in Ipomoea series Batatas suggested that Ipomoea Carolina morphotype may be Ipomoea grandifolia, a species described as found only in South America. To evaluate these findings, we tested intrinsic cross-compatibility between Ipomoea Carolina morphotype and I. grandifolia as well as with three other co-localizing North American Ipomoea species – Ipomoea cordatotriloba, Ipomoea lacunosa, and Ipomoea leucantha. We also examined genetic differentiation using single nucleotide polymorphisms from leaf transcriptomes from multiple individuals of all five species and several outgroup species. We find no cross-incompatibility and little genetic differentiation between Ipomoea Carolina morphotype and Ipomoea grandifolia, suggesting that Ipomoea Carolina morphotype is a representative of Ipomoea grandifolia. This finding raises additional questions about the origins of Ipomoea grandifolia in North America and how its disjunct distribution could play a role in the divergence of Ipomoea grandifolia in the future.