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

Crataegus bretschneideri is considered a variety of Crataegus pinnatifida,
but it 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 interence and
neighbor-joining molecular phylogenetic tree analysis with 108 individuals
of 19 hawthorn (Crataegus) species and 4 outgroups (Malus). ITS, cpDNA and
cpDNA-ITS molecular phylogenetic trees constructed using 4 methods have
similar consistency respectively. In the cpDNA-ITS molecular phylogenetic
tree, C. bretschneideri is an independent clade separated from Crataegus
maximowiczii and C. pinnatifida, which provides a separate species
condition. In the ITS (nuclear inheritance) molecular phylogenetic tree,
C. bretschneideri and C. pinnatifida are closely related and are distantly
related to C. maximowiczii. The cpDNA (maternal inheritance) molecular
phylogenetic tree indicated that C. bretschneideri is closely related to
C. maximowiczii but distantly related to C. pinnatifida. Furthermore, the
108 Crataegus individuals belonged to 15 chloroplast haplotypes, as
determined using the DNASP analysis; C. bretschneideri and C. maximowiczii
have the same chloroplast haplotype, H1; C. pinnatifida contains three
haplotypes, H13-H15. Taken together with previous results of our
laboratory, 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.