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

Enkianthus (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 Enkianthus. 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 Andromedina, Enkiantella, Enkianthus, and Meisteria, with sect. Enkianthus as the first diverging clade. Divergence time analysis supported an ancient origin of Enkianthus 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 Enkianthus. These results will provide invaluable information for further population-level studies on species delimitation and adaptive evolution in Enkianthus, and will benefit Enkianthus conservation and utilization.