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Background The genus Ligusticum consists of approximately 60 species distributed in the Northern Hemisphere. It is one of the most taxonomically difficult taxa within Apiaceae, largely due to the varied morphological characteristics. To investigate the plastome evolution and phylogenetic relationships of Ligusticum, we determined the complete plastome sequences of eight Ligusticum species using a de novo assembly approach. Results Through a comprehensive comparative analysis, we found that the eight plastomes were similar in terms of repeat sequence, SSR, codon usage, and RNA editing site. However, compared with the other seven species, L. delavayi exhibited striking differences in genome size, gene number, IR/SC borders, and sequence identity. Most of the genes remained under the purifying selection, whereas four genes showed relaxed selection, namely ccsA, rpoA, ycf1, and ycf2. Non-monophyly of Ligusticum species was inferred from the plastomes and internal transcribed spacer (ITS) sequences phylogenetic analyses. Conclusion The plastome tree and ITS tree produced incongruent tree topologies, which may be attributed to the hybridization and incomplete lineage sorting. Our study highlighted the advantage of plastome with mass informative sites in resolving phylogenetic relationships. Moreover, combined with the previous studies, we considered that the current taxonomy system of Ligusticum needs to be improved and revised. In summary, our study provides new insights into the plastome evolution, phylogeny, and taxonomy of Ligusticum species.

The genus Allium (Amaryllidaceae, Allioideae) is one of the largest monocotyledonous genera and it includes many economically important crops that are cultivated for consumption or medicinal uses. Recent advances in molecular phylogenetics have revolutionized our understanding of Allium taxonomy and evolution. However, the phylogenetic relationships in some Allium sections (such as the Allium section Daghestanica ) and the genetic bases of adaptative evolution, remain poorly understood. Here, we newly assembled six chloroplast genomes from Chinese endemic species in Allium section Daghestanica and by combining these genomes with another 35 allied species, we performed a series of analyses including genome structure, GC content, species pairwise Ka/Ks ratios, and the SSR component, nucleotide diversity and codon usage. Positively selected genes (PSGs) were detected in the Allium lineage using the branch-site model. Comparison analysis of Bayesian and ML phylogeny on CCG (complete chloroplast genome), SCG (single copy genes) and CDS (coding DNA sequences) produced a well-resolved phylogeny of Allioideae plastid lineages, which illustrated several novel relationships with the section Daghestanica . In addition, six species in section Daghestanica showed highly conserved structures. The GC content and the GC3s content in Allioideae species exhibited lower values than studied non-Allioideae species, along with elevated pairwise Ka/Ks ratios. The rps2 gene was lost in all examined Allioideae species, and 10 genes with significant posterior probabilities for codon sites were identified in the positive selection analysis, seven of them are associated with photosynthesis. Our study uncovered a new species relationship in section Daghestanica and suggested that the selective pressure has played an important role in Allium adaptation and evolution, these results will facilitate our further understanding of evolution and adaptation of species in the genus Allium .

Lineage persistence and explosive radiation were important processes for establishing high species diversity of Lilieae in the QTP region. Both long-distance dispersal and migration across Beringia probably contributed to the modern distribution range of Lilieae. Our study shows that biotic interchanges between the QTP region and Irano-Turanian region and the Mediterranean Basin were bi-directional, suggesting the latter was a secondary centre of diversity.

Background and Aims The genus Allium L., one of the largest monocotyledonous genera and one that includes many economically important crops with nutritional and medicinal value, has been the focus of classification or phylogeny studies for centuries. Recent studies suggested that the genus can be divided into 15 subgenera and 72 sections, which were further classified into three evolutionary lineages. However, the phylogenetic relationships reconstructed by one or two loci showed weaker support, especially for the third evolutionary lineage, which might not show the species relationships very clearly and could hinder further adaptive and evolutionary study. Methods In this study, a total of 39 complete chloroplast genomes of Allium (covering 12 Allium subgenera) were collected, and combining these with 125 species of plastomes from 19 other families of monocots, we reconstructed the phylogeny of the genus Allium, estimated the origin and divergence time of the three evolutionary lineages and investigated the adaptive evolution in this genus and related families. Results Our phylogenetic analysis confirmed the monophyly and three evolutionary lineages of Allium, while new species relationships were detected within the third evolutionary lineage. The divergence time of the three evolutionary lineages was estimated to be in the early Eocene to the middle Miocene, and numerous positive selected genes (PSGs) and PSGs with high average Ka/Ks values were found in Allium species. Conclusions Our results detected a well-supported phylogenetic relationship of Allium. The PSGs and PSGs with high Ka/Ks values, as well as diversified morphologies, complicated chromosome characteristics and unique reproductive modes may play important roles in the adaptation and evolution of Allium species. This is the first study that conducted phylogenetic and evolutionary analyses on the genus Allium combined with the plastome and morphological and cytological data. We hope that this study can contribute to further analysis of Allium for other researchers.