Landscape genomics and demography of California Azolla

Abstract

Azolla was collected and sequenced across California as a part of the California Conservation Genomics Project. We identify three major populations of Azolla in the state. Out of these groups, we are able to confidently identify one as Azolla filiculoides. The other two taxa are seemingly newly reported to California and are not the same as the taxa currently treated by the Jepson Manual; specifically, they are not members of the A. microphylla/mexicana clade. We infer patterns of Azolla genetic diversity across the state and the demographic histories of these populations. We find evidence that both isolation by distance and isolation by environment contribute to spatial genetic variation. Both of the two newly reported populations have demographic histories consistent with recent invasions of the state. However, we also discuss alternative possibilities and propose a roadmap for resolving the taxonomy of California Azolla.