关键词: 变叶海棠, 物种复合体, 物种界定, 遗传分化, 单拷贝核基因

Abstract: Based on the elucidation of genetic origins of taxa in the Malus toringoides species complex，
species delimitation and genetic divergence of this species complex were studied using single-copy nuclear
gene SbeⅠ. There are three main clades on the maximum likelihood tree constructed with SbeⅠ. Species
delimitation analyses indicated that the three clades correspond to three species. However，taxa within the
three clades cannot be delimited as species except M. transitoria. The results of species delimitation were
further supported by the estimation of genetic distance and fixed index. Within a clade，the range of genetic
distances（0–0.006）between sequences from the same taxa is overlapped with those from different taxa.
While genetic distances（0.008–0.016）between sequences from different clades are larger than those from
the same clade. The estimation of fixed index is consistent with the estimated genetic distance. These
analyses showed that the genetic divergence between taxa within a clade is rather small，and taxa within the
same clade shouldn’t be delimited as species. Based on the results of species delimitation，the estimation of genetic divergence，and the genetic origin of taxa in the M. toringoides species complex，it would be better
to recognize M. × setok as the variant of M. × toringoides，and to recognize M. × maerkangensis and M. ×
xiaojinensis as a single agamospeciesin the species complex. Species delimitation in the M. toringoides
species complex could shed light on the utilization and protection of wild resource in genus Malus.

Key words: Malus toringoides, species complex, species delimitation, genetic divergence, single-copy nuclear gene