Abstract:Previous taxonomic treatments in Russia and China have considered Corylus mandshurica and C. sieboldiana to be distinct as independent species. A morphometric analysis was conducted to determine if the morphological differentiation from these taxa warrants specific taxonomic recognition with a large sample of field-collected leaves as well as specimens from several herbaria of northeastern Asia. One hundred and fifty two individuals representing Chinese, Korean, and Japanese geographic ranges of the species were scored for 18 morphological characters and the data matrix was used for principal components analysis. The entities that comprise C. sieboldiana complex exhibit widely overlapping ranges in all morphological attributes. The leaf and fruit data may reflect a lack of divergence between taxa. Therefore, we do not regard these to be sufficient for taxonomic splitting of C. mandshurica from C. sieboldiana to warrant the designation of the rank of a species based on morphology. The two taxa were not morphologically well differentiated and their ranges of distribution come together. Therefore, C. mandshurica should be recognized as an infraspecific taxon of C. sieboldiana. C. sieboldiana with short involucres in southern Korea and Japan is often treated as an independent species （C. hallaisanensis） or a variety (C. sieboldiana var. brevirostris), but should be only recognized as a form of C. sieboldiana because this involucral character is highly variable even within the same individual.