Cheadle Center for Biodiversity and Ecological Restoration

Delimiting biodiversity units is challenging when hybridization, plasticity, and other factors blur visible boundaries, and it is especially difficult for subspecies, which remain poorly defined in the genomics era. Eastwood manzanita (Arctostaphylos glandulosa) is a widespread, morphologically complex shrub with 10 recognized subspecies that often overlap geographically and show frequent intermediates; delimitation matters because two subspecies are rare. We combined public environmental geospatial data with reduced-representation genome sequencing to test genetic and environmental differentiation and to evaluate whether subspecies can be separated by environmentally associated genetic variation. We found little to no genetic differentiation among most subspecies, except for one of the rare subspecies, and environmental analyses showed no clear ecological separation (with important analytical limitations). Overall, genetic structure aligns more with geography than current subspecies boundaries, suggesting subspecies concepts may need rethinking for long-lived plants in the era of next-generation sequencing.