Aims Hybridization usually leads to gene introgression between related spe-cies in hybrid zones,associated with complex patterns of morpho-logical variation.Nevertheless,previous studies have tended to ignore the effects of geographic variation in hybridization rates on species taxonomy.This study aims to investigate the variation of morphologi-cal traits between two sympatric and taxonomically confused oak spe-cies,Quercus liaotungensis and Q.mongolica,and reveal the effects of hybridization rates on morphological traits and the taxonomic boundary.Methods We used seven microsatellite loci to evaluate species status and measured 15 morphological traits in 26 trees in the recent hybrid zone between Q.liaotungensis and Q.mongolica,and we char-acterized the differences between the two oak species and their hybrids for the investigated traits.Important Findingsmolecular analyses indicated that 74%of 78 sampled maternal trees were hybrids between Q.liaotungensis and Q.mongolica although the observed morphological variation suggested that they had remained distinct species.across all of the differentiated leaf and reproductive traits,the hybrids expressed patterns similar to Q.liaotungensis,which may suggest dominant expression of paren-tal characters.These results are consistent with our expectation that hybrids will be difficult to distinguish from parental species in a recent hybrid zone.
