Repetita iuvant. The extraordinary evolutionary history of the endemic palm Chamaerops humilis L. in the Mediterranean

Chamaerops humilis L. is the only Arecaceae species endemic to the western Mediterranean. Here, de novo genome sequencing allowed discovering reasons behind its exclusive persistence within the natural distribution area, although the troubled environmental changes occurred. The genome, estimated at 3.44 Gbp, and its annotation enabled the identification of 60,555 genes and 2.87 Gbp of repetitive regions. Evolutionary analyses revealed a whole-genome duplication event 48.02 mya, shared with other palm species, and a later divergence from Phoenix dactylifera (17 mya). The characterization of gene duplication types, and the distribution of K _S values, uncovered multiple recent duplication waves, and the presence of C. humilis -specific duplicated genes involved in responses to stress. Furthermore, expansions of transposable elements were detected and appear to be associated with major paleoclimatic events in the Mediterranean. These genomic features likely contributed to the resilience and long-term survival of C. humilis within the Mediterranean.