Plastid genomes reveal evolutionary shifts in elevational range and flowering time of (Oleaceae).

Species of are economically important ornamental trees, yet information regarding their plastid genomes (plastomes) have rarely been reported, thus hindering taxonomic and evolutionary studies of this small but enigmatic genus. Here, we performed comparative genomics and evolutionary analyses on plastomes of 16 of the 28 currently accepted species, with 11 plastomes newly sequenced. Phylogenetic studies identified four main lineages within the genus that are here designated the: "Caucasian " (corresponding to . ), "" (corresponding to . sect. ), ".  + ," and "Core : (corresponding to . sect.  + . sect. ). Molecular clock analysis suggested that split from its sister clade c. 15.83 Ma. The estimated crown ages of the lineages were the following: genus at 12.66 Ma; "" clade at 5.85 Ma; ".  + " at 4.89 Ma; and "Core : clade at 6.2 Ma. Ancestral state reconstructions and trait mapping showed that ancestors of were spring flowering and originated at lower elevations. Phylogenetic principal component analysis clearly distinguished spring-flowering species from autumn-flowering species, suggesting that flowering time differentiation is related to the difference in ecological niches. Nucleotide substitution rates of 80 common genes showed slow evolutionary pace and low nucleotide variations, all genes being subjected to purifying selection.