Geographically proximate rare species exhibit strong population divergence while maintaining intraspecific genetic diversity in Homoranthus (Myrtaceae)

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BACKGROUND AND AIMS: Species with small geographical ranges provide insights into adaptation, speciation and genetic drift, while also presenting clear conservation challenges. Homoranthus A.Cunn. ex Schauer (Myrtaceae), an Australian genus with many narrow endemics, offers a model for understanding how ecological and spatial factors drive diversification. We examined a regional hotspot with a high number of Homoranthus narrow endemics to assess patterns of genetic diversity and inform both evolutionary understanding and conservation planning. METHODS: We generated genome-wide single-nucleotide polymorphism data using DArTseq for 282 individuals across 13 Homoranthus species (40 % of the genus), including 10 narrow endemics, to assess population genetic structure and diversity. KEY RESULTS: All species showed strong genetic isolation, even over a few kilometres, with populations diverging within hundreds of metres. Homoranthus lunatus includes two highly divergent, non-sister lineages, suggesting taxonomic revision. Inbreeding was common but unrelated to range size, and heterozygosity remained moderate, indicating intrinsic buffering of genetic diversity. Genome sizes were notably small relative to other angiosperms. CONCLUSIONS: Ecological isolation, life-history traits, and limited dispersal drive both speciation and extinction risk in Homoranthus. Diversification and endemism are linked to spatial isolation, highlighting the need for conservation strategies that address ecological connectivity in addition to species protection.

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