Abstract: Apomixis can confer fertility upon spontaneous hybrids and allopolyploids, both of which have played a pivotal role in the evolutionary trajectory and diversification of flowering plants. We hypothesized that an unusual morphotype of Elatostema represents a viable hybrid species between E. scabrum and E. hirticaule, as opposed to a sterile F1 hybrid. To test this, we employed phylogenomic, flow cytometry (FC), cytological, and morphological analyses. A two-step phylogenomic approach was used. Genome skimming was performed on one E. longpingii population, three populations of each parent (E. scabrum, E. hirticaule), and ten Elatostema and one Pilea species. Population genetic analyses were then conducted using RAD sequencing data from the type population of hybrid and parent species. Phylogenomic analyses using genome skimming and RAD sequencing data consistently supported a hybrid origin, placing E. longpingii close to or nested within E. scabrum and distant from E. hirticaule. Chromosome counts revealed pentaploid, triploid, and tetraploid ploidy levels in E. longpingii, E. scabrum, and E. hirticaule, respectively. FC suggested apomixis in E. longpingii and E. scabrum, while E. hirticaule exhibited sexual reproduction. Morphological studies indicated that E. longpingii shares traits from both parents. Our findings demonstrate a novel reproductively viable hybrid species in Elatostema, likely originated through a natural hybridization event involving heteroploidy, coupled with the inheritance of an apomictic reproductive pathway from its maternal parent. These results provide compelling evidence that hybridization and apomixis have played pivotal roles in driving reticulate evolution and promoting diversification within the Elatostema.

Key words: analysis, apomixis, morphology, natural hybridization, Pellionia, phylogenomic new species