Dipteronia Oliv. is an endangered genus found in China with two species, D. sinensis and D. dyeriana. Previous morphological, cytogenetic, and molecular studies have suggested that D. dyeriana is a species related to D. sinensis. However, it is unclear how the two species diverged and whether gene flow exists between these two species. Here, we performed a molecular study at the population level to characterize genetic differentiation and decipher the phylogeographic history for Dipteronia species based on newly sequenced chloroplast DNA (cpDNA) and amplified fragment length polymorphisms (AFLP) date retrieved from our previous studies. No haplotype was shared between the two species in the cpDNA network. However, the phylogenetic analysis suggested that a haplotype found in D. sinensis (H4) showed a closer relationship with haplotypes of D. dyeriana. Based on our estimated time of divergence, these two cpDNA haplotype lineages of Dipteronia diverged at about 31.19 Ma. Furthermore, two genetic clusters with asymmetric gene flow were supported based on the structure analysis, which corresponded with the two Dipteronia species, and we also detected a low level of asymmetric gene flow between these two species according to the MIGRATE analysis using AFLP data. During the Last Glacial Maximum (LGM, c.21 kya BP), the genus’ predicted distribution was more or less similar to that at present, which was also supported by the mismatch analyses that showed no population expansion of the two Dipteronia populations after the LGM. The combined cpDNA and AFLP data revealed significant genetic differentiation between the two Dipteronia species with asymmetric gene flow, which can be explained by the varying phylogeographical histories of these two species.

Knowledge of interspecific divergence and population expansions/contractions of dominant forest trees in response to geological events and climatic oscillations is of major importance to understand their evolution and demography. However, the interspecific patterns of genetic differentiation and spatiotemporal population dynamics of three deciduous Cerris oak species (Q. acutissima, Q. variabilis and Q. chenii) that are widely distributed in China remain poorly understood. In this study, we genotyped 16 nuclear loci in 759 individuals sampled from 44 natural populations of these three sibling species to evaluate the plausible demographical scenarios of the closely related species. We also tested the hypothesis that macro- and microevolutionary processes of the three species had been triggered and molded by Miocene–Pliocene geological events and Quaternary climatic change. The Bayesian cluster analysis showed that Q. acutissima and Q. chenii were clustered in the same group, whereas Q. variabilis formed a different genetic cluster. An approximate Bayesian computation (ABC) analyses suggested that Q. variabilis and Q. acutissima diverged from their most common ancestor around 19.84 Ma, and subsequently Q. chenii diverged from Q. acutissima at about 9.6 Ma, which was significantly associated with the episodes of the Qinghai–Tibetan Plateau (QTP). In addition, ecological niche modeling and population history analysis showed that these three Cerris oak species repeatedly underwent considerable ‘expansion–contraction’ during the interglacial and glacial periods of the Pleistocene, although they have varying degrees of tolerance for the climatic change. Overall, these findings indicated geological and climatic changes during the Miocene–Pliocene and Pleistocene as causes of species divergence and range shifts of dominant tree species in the subtropical and warm temperature areas in China.

Symphytum officinale is a perennial herb belonging to the Boraginaceae. Here, we sequenced the complete chloroplast (cp) genomes of S. officinale using Illumina sequencing technology. The results revealed that the cp genome is 148,149 bp in length and exhibits a typical quadripartite structure, with a pair of inverted repeat regions (IR) comprising 27,001 bp, a large single-copy (LSC) region comprising 77,366 bp, and a small single-copy (SSC) region comprising 16,781 bp. The sequence contained 133 unique genes, including 86 protein-coding genes, 37 transfer RNAs, eight ribosomal RNAs, and two pseudogenes. Six tandem, 42 dispersed, and 38 simple sequence repeats were identified. Sequence divergence analysis across 21 Boraginaceae species revealed that the most divergent regions, potentially serving as specific DNA barcodes, were found in non-coding spacers. A comparative analysis of the IR/SC boundary regions of the 21 Boraginaceae species revealed IR expansion events in S. officinale. Phylogenetic analysis based on 63 protein-coding genes demonstrated that S. officinale was closely related to Nonea vesicaria. This represents the first cp genome sequenced in Symphytum, and our results provide valuable genetic information for future population and phylogenetic studies of Boraginaceae.