The extent to which hybridization leads to gene flow between plant species depends on the structure of hybrid populations. To assess possible variation in a hybrid population structure, Yan et al. evaluate magnitude and direction of natural hybridization between two diploid Chinese endemic species Rhododendron spiciferum and R. spinuliferum.
Thirteen nuclear microsatellites and cpDNA trnL-F were employed to characterize the genetic structure of 566 individuals collected from 15 non-allopatric populations and nine allopatric parental populations. Gene flow between R. sjpiciferum and R. spinuliferum is found to be bidirectional and asymmetric in some hybrid swarms. Introgression, rather than hybrid speciation, is a more likely outcome of hybridization between these hybridizing taxa.