Complete Chloroplast Genome of <i>Enkianthus</i> Lour. (Ericaceae): Comparative Analysis, Phylogenetic Relationships, Divergence History, and Adaptive Evolution

<i>Enkianthus</i> (Ericaceae) is a small genus of great ornamental and ecological importance, preferring the specialized habitats in montane elfin forests of east Asia. Here, we for the first time sequenced, assembled, and annotated the complete chloroplast genomes of 16 species, representing all four sections of <i>Enkianthus</i>. The plastomes exhibited a typical quadripartite structure and were highly conserved in genome size, organization, and gene content. Plastid phylogenomics confirmed the monophyly of four sections of <i>Andromedina</i>, <i>Enkiantella</i>, <i>Enkianthus</i>, and <i>Meisteria</i>, with sect. <i>Enkianthus</i> as the first diverging clade. Divergence time analysis supported an ancient origin of <i>Enkianthus</i> at the Late Cretaceous but rapid recent radiation since the Lat-Miocene onward. Selection pressure analysis detected 12 positively selected genes, which might be linked to adaptive evolution in <i>Enkianthus</i>. These results will provide invaluable information for further population-level studies on species delimitation and adaptive evolution in <i>Enkianthus</i>, and will benefit <i>Enkianthus</i> conservation and utilization.