Conservation genomics of Lompoc yerba santa (Eriodictyon capitatum, Namaceae), including phylogenomic insights into the evolution of Eriodictyon

Eriodictyon capitatum (Namaceae) is a narrowly distributed shrub endemic to western SantaBarbara County, where it is known from only 10 extant California Natural Diversity Database(CNDDB) Element Occurrences (EOs). Owing to low numbers of plants in nature, a limitedoverall areal extent, and multiple current threats, E. capitatum is listed as Endangered under theFederal Endangered Species Act, as Rare under the California Native Plant Protection Act, andhas been given the California Rare Plant Rank of 1B.2 by the California Native Plant Society. Inthe present study, high throughput DNA sequence data were analyzed to investigate geneticdiversity within and among all accessible EOs; to determine the extent of genetic isolation amongEOs; to examine clonality within EOs; and to examine the taxonomic circumscriptions of E.capitatum, E. altissimum, E. angustifolium, and E. californicum through phylogenomic analysis.Population genetic analyses of E. capitatum reveal a pattern of strong genetic differentiation bylocation/EO. The clonality assessment provides the potentially novel insight that certain small EOsmay support relatively few multilocus genotypes. The phylogenomic analyses strongly support thepresent-day taxonomic circumscriptions of both E. altissimum and E. capitatum, showing them tobe reciprocally monophyletic and sister with strong support. Taken together, these results paint apicture of an evolutionarily and morphologically distinct species known from relatively few,genetically isolated stations. Conservation recommendations are made in consideration of thesefindings.