Comparative analyses of the plastid genomes and their phylogenetic implications in tribe delphinieae (Ranunculaceae)

BACKGROUND: The tribe Delphinieae (Ranunculaceae) has long posed challenges in terms of both its phylogeny and its taxonomy. This study integrates 60 newly sequenced plastid genomes with 57 published ones (117 in total) to construct a robust evolutionary framework for the tribe. RESULTS: Our analyses reveal that the plastomes of Delphinieae exhibit exceptional structural conservation, contrary to the frequent rearrangements observed in related Ranunculaceae lineages. The plastid phylogenomic framework resolves long-standing controversies, providing maximum support for all major intergeneric relationships (bootstrap support (BS) = 100; posterior probability (PP) = 1.0). Our results place the annual genus Staphisagria as the earliest-diverging lineage, sister to the remainder of the tribe. The results also identify Gymnaconitum as the sister genus to Delphinium. This topology challenges the traditional view of life-history evolution by strongly supporting a transition from an annual to a perennial habit within the tribe, a hypothesis corroborated by the annual nature of its outgroups. Divergence time estimates indicate that the major radiations of the two largest subgenera, Aconitum subg. Aconitum and Delphinium subg. Delphinastrum, occurred from the mid- to late Miocene, coinciding with major geological and climatic shifts. CONCLUSIONS: This study provides a definitive phylogenetic backbone for Delphinieae, clarifies its life-history evolution, and links its diversification to key geological events. The conserved plastome structure and identified hypervariable regions offer a foundation for future systematic and population-level studies in this ecologically and medicinally important tribe.