Chloroplast DNA sequences are widely employed markers in plant species delimitation and phylogenetics.However, chloroplast DNA (cpDNA) sequence variants might be shared among closely related species due to incomplete sorting of ancestral lineages and interspecific hybridization.In this study, we sequenced five chloroplast fragments (trnH–psbA, rpL14–rpL36, trnQ–trnS, trnS–trnT and trnL–trnF) in 160 samples from 33 populations representing ten species of Chinese white oak.
Results/Conclusions
The concatenated cpDNA sequences had a total length of 4435 bp, in which 41 sites were variable across all individual samples, with 15 indels and 26 substitutions. In combination, these polymorphisms identified a total of 31 haplotypes. For the oak populations located in north China, different species often shared the same cpDNA haplotypes when in sympatry or neighborhood populations, whereas distant geographic populations of the same species had different haplotypes. Most populations in south China hold specific haplotypes, with the exception of haplotype H19, which was shared by sympatric Quercus fabri and Q. aliena var. acuteserrata populations in Tianmu mountain of Zhejiang province, and haplotype H21, which was shared by Q. fabri in Tianmu mountain of Zhejiang province, Quercus serrata from Zhangjiajie, Hunan province, and Q. liaotungensis and Quercus mongolica in Tonghua, Jilin province. Spatial Analysis of Molecular Variance (SAMOVA) divided all oak populations into six groups, mainly according to their geographic locations rather than species classifications. The proportion of cpDNA variation among these groups was estimated as 66.04%, while the proportion of variation among species was only estimated as 9.57%. The neighbor-joining tree for all haplotypes shows haplotypes from the same geographical group tended to cluster together, whereas haplotypes from the same species always scattered into different clades.These results indicated that chloroplast DNA variants across Chinese white oak species cannot reflect interspecific divergence, but is related to their geographic. As a result, studies that rely on variations of chloroplast DNA between species to explain their distinctness and phylogenetics are not applicable in such taxa as Chinese white oaks, which has widespread interspecific hybrid or incomplete lineage sorting.