The Phylogenetic Analysis of Two Invasive Trapa Species in the United States Revealed by Chloroplast Genomes and Morphological Traits

Knowledge of the phylogenetic relationship for invasive plants is conducive to understanding their invasion pathways. USA possesses two invasive Trapa species, Trapa natans L. and T. bispinosa Roxb. var. iinumai Nakano. The former has four-spined nuts and white flowers, while the latter has two-spined nuts and pink flowers. The chloroplast (cp) genomes of the two species were initially sequenced and showed different genome sizes with 155,547 bp and 155,675 bp for T. natans and T. bispinosa var. iinumai , respectively. Phylogenetic analyses showed that the two American Trapa species belonged to different branches of the large-seed Trapa plants. A close genetic relationship was detected between American T. natans and Chinese T. litwinowii , which possessed prominent fruit neck and crown; by contrast, a distant evolutionary relationship was found between T. bispinosa var. iinumai and the others. Findings of this study support that two introductions of Trapa into North America have occurred. It is important to understand the phylogenetic relationships for this genus and the implications for conservation of Trapa spp. in native regions, and prevention of further range expansion and management of Trapa spp. in invaded areas.