Studies in Eastwood manzanita, Arctostaphylos glandulosa, with Glen Morrison: Delimiting biodiversity units is difficult in organisms in which differentiation is obscured by hybridization, plasticity, and other factors that blur phenotypic boundaries. Such work is more complicated when the focal units are subspecies, the definition of which has not been broadly explored in the era of modern genetic methods. Eastwood manzanita (Arctostaphylos glandulosa Eastw.), is a widely distributed and morphologically complex chaparral shrub species with much subspecific variation that has proven challenging to categorize. Currently ten subspecies are recognized, however, many of them are not geographically segregated, and morphological intermediates are common. Subspecies delimitation is of particular importance in this species, as two of the subspecies are rare. In this study, we applied an evolutionary definition of subspecies, reduced-representation genome sequencing, and environmental data, to evaluate differentiation within Eastwood manzanita. Our analyses did not show genetic differentiation among subspecies of Eastwood manzanita, with the exception of one of the two rare subspecies, San Gabriel manzanita (A. glandulosa subsp. gabrielensis). We present further exploration of the genetic distinction of San Gabriel manzanita, and use our sequence data to evaluate an existing hypothesis that San Gabriel manzanita may be of hybrid origin between A. glandulosa and a second species, A. parryana.