Japanese climbing fern (Lygodium japonicum) invasion in the U.S.; insights from chloroplast genome sequencing

Japanese climbing fern (Lygodium japonicum) is a vine native to the open forests of eastern Asia that has become an invasive species in the U.S. Herbarium records first note this species in the U.S. in 1903 (Georgia), with spread to eight states by the end of the 1930s and current establishment in 10 states of the southeastern U.S. We aimed to ask three questions regarding the introduction of L. japonicum: (1) Was there a single Japanese climbing fern introduction or were there multiple introductions? (2) What is the distribution of genotypes in the U.S.? and (3) What are the source population(s) from the native range in Asia? We sequenced the chloroplast genome from 74 L. japonicum herbarium specimens representing 24 native and 50 invasive range populations. Seventeen haplotypes were found in the native range compared to three in the invasive range. Our results indicate L. japonicum has low genotypic diversity in the invasive range relative to the native range. Even with low genotypic diversity, these data suggest at least three introductions of L. japonicum. However, we were unable to define the native source population(s) of invasive L. japonicum.