Genomic and population genomic analyses reveal contrasting diversity and demographic histories in a critically endangered and a widespread Oreocharis species

Preserving genetic diversity is crucial for the long-term survival of wild plant species, yet many remain at risk of genetic erosion due to small population sizes and habitat fragmentation. Here, we present a comparative genomic study of the critically endangered <i>Oreocharis esquirolii</i> (Gesneriaceae) and its widespread congener <i>O. maximowiczii</i>. We assembled and annotated chromosome-level reference genomes for both species and generated whole-genome resequencing data from 28 <i>O. esquirolii</i> and 79 <i>O. maximowiczii</i> individuals. Our analyses reveal substantially lower genetic diversity and higher inbreeding in <i>O. esquirolii</i>, despite its overall reduced mutational burden. Notably, <i>O. esquirolii</i> exhibits an elevated proportion of strongly deleterious mutations relative to <i>O. maximowiczii</i>, suggesting that limited opportunities for purging have allowed these variants to accumulate. These contrasting genomic profiles likely reflect divergent demographic histories, with <i>O. esquirolii</i> having experienced severe bottlenecks and protracted population decline. Collectively, our findings highlight the critically endangered status of <i>O. esquirolii</i>, characterized by diminished genetic diversity, pronounced inbreeding, and reduced ability to eliminate deleterious alleles. This study provides valuable genomic resources for the Gesneriaceae family and underscores the urgent need for targeted conservation measures, including habitat protection and <i>ex situ</i> preservation efforts, to mitigate the extinction risk facing <i>O. esquirolii</i> and potentially other threatened congeners.