Crataegus bretschneideri (Rosaceae), a separate species endemic to northeast China

Abstract

Crataegus bretschneideri has been considered a variety of Crataegus pinnatifida, but has also been proposed as a separate species. We used ITS and three cpDNA sequence fragments (psbA‐trnH, trnG‐trnS, trnH‐trnK) to perform maximum parsimony, maximum likelihood, Bayesian inference and neighbor‐joining molecular phylogenetic analysis on 108 individuals of 19 hawthorn (Crataegus) species and 4 outgroups (Malus). The ITS, cpDNA and cpDNA‐ITS molecular phylogenetic trees constructed using 4 methods had similar consistency.In the cpDNA‐ITS tree, C. bretschneideri was resolved as an independent clade separated from Crataegus maximowiczii and C. pinnatifida. In the ITS (biparental inheritance) tree, C. bretschneideri and C. pinnatifida were resolved as closely related and only distantly related to C. maximowiczii. In contrast, the cpDNA (maternal inheritance) tree indicated that C. bretschneideri is closely related to C. maximowiczii but distantly related to C. pinnatifida. In total, 15 chloroplast haplotypes were revealed in the 108 Crataegus individuals, as determined by DNASP analysis. Of these, C. bretschneideri and C. maximowiczii share the same chloroplast haplotype, H1, while C. pinnatifida contains three haplotypes, H13–H15. Taken together with previous results, we confirm that C. bretschneideri is not a variety of C. pinnatifida, but a separate species that gradually developed from natural hybrid offspring in mixed forest areas with C. maximowiczii as the female parent and C. pinnatifida as the male parent.