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.

We made pairwise crosses between individuals of these species: Ipomoea Carolina morphotype, Ipomoea grandifolia, Ipomoea cordatotriloba, Ipomoea lacunosa, and Ipomoea leucantha to examine cross-compatibility in the form of seed set. We calculated summary statistics and fitted linear models to test for any reproductive barriers to seed set.

We also examined genetic differentiation using single nucleotide polymorphisms (SNPs) from leaf transcriptomes from multiple individuals of all five species and several outgroup species. We extracted RNA, had libraries made and sequenced, aligned all reads to the I. lacunosa draft genome, called SNPs, and performed cluster analyses in the form of PCA, neighbor-joining trees, and fastSTRUCTURE and ADMIXTURE.

Most files, datasets, and scripts, can be found on https://github.com/itliao/Grandifolia (also via the linked zenodo URL). All other files are found here, found in dryadREADME.txt.

In all raw files, Ipomoea Carolina morphotype is referred as Ipomoea "austinii."