Interspecific hybridization in North American Polygala (Polygalaceae)

As a part of ongoing systematic and phylogenetic studies in Polygalaceae, field collections of two pairs of North American species (Polygala balduinii and P. ramosa, and P. lutea and P. rugelii) had morphologically intermediate forms and grew sympatrically, and so were suspected to be interspecific hybrids. Although hybrids among plants are often invoked in taxonomic and floristic literature based on morphologic intermediacy, they are rarely documented and substantiated using molecular tools. We found that the morphologically intermediate individuals within intermixed populations of both species pairs did indeed share all of the variable nucleotide sites in nrITS among the parent species. Likewise, using plastid sequence data (trnL-F), we determined that in both species pairs, the parentage was bidirectional. Although some DNA inheritance phenomena (e.g. incomplete lineage sorting) can result in similar polymorphic DNA sequence data, the intermediacy in both morphology and sequence data within sympatric populations is more indicative of interspecific hybridization.