Molecular phylogenetics uncovers previously unrecognized Mexican diversity within the pantropical Cassytha filiformis complex

Abstract Cassytha filiformis is a hemiparasitic species of Lauraceae with a pantropical distribution and subtle morphological variation across its range. In Mexico, populations traditionally assigned to C. filiformis occur disjunctly in coastal dune systems of the Yucatan Peninsula and in inland habitats of western and southern Mexico. To investigate their evolutionary relationships within a global context, we sequenced four complete plastomes from Chiapas, Jalisco, Quintana Roo, and Yucatan (one accession per state) and generated nuclear ITS sequences for 40 individuals representing eight populations. Phylogenomic analyses recovered C. filiformis sensu lato as monophyletic assemblage comprising three major evolutionary lineages: an Asian lineage, a Tropical widespread lineage spanning Asia, Africa, and the Americas, and a deeply divergent lineage endemic to western Mexico. Mexican populations were not recovered as a single monophyletic group; instead, populations from the Yucatan Peninsula (Quintana Roo, and Yucatan) and Chiapas clustered with Caribbean accessions, whereas western Mexican populations formed an early-diverging lineage. Divergence-time analyses indicate that the western Mexican lineage has remained evolutionarily isolated since the early Miocene (ca. 23.75 Ma). The congruence between plastome and nuclear datasets, together with consistent morphological and ecological differences, supports the recognition of this lineage as the reinstated species Cassytha brachystachya (Meisn.) Ruiz-Sanchez & L. Perez. Our results demonstrate that C. filiformis , as traditionally circumscribed, represents a geographically structured species complex and illustrate how integrative phylogenomics can uncover overlooked diversity within widespread tropical plants.