Chromosome-level genome and population genomics reveal demographic history, incomplete divergence and coastal adaptation of Rhododendron simsii var. putuoense in East China

• First chromosome-level genome assembly of Rhododendron simsii var. putuoense (479.30 Mb, contig N50 = 33.97 Mb, 98.4 % BUSCO), advancing Ericaceae genomics. • 21 populations form coastal-island genetic groups with incomplete divergence, moderate diversity, gene flow; island groups show stronger selection and inbreeding. • Adaptive evolution via WGD, expanded secondary metabolite gene families, and positively selected salt/cold tolerance genes, revealing coastal multi-stress strategies.