Morphological and genetic survey of Giant Salvinia populations in Louisiana and Texas

•Trait and gene diversity of Giant Salvinia were examined in Louisiana and Texas.•Significant variation was detected for morphological traits in both collection sites.•The majority of molecular variation was found within rather than among population.•Giant Salvinia in Louisiana and Texas was derived from the same clonal population. Giant Salvinia (Salvinia molesta Mitchell) is a floating aquatic fern introduced from South America whose rapid growth impairs health of plants and animals in lakes, rivers, and bayous in various southern U.S. states. To assist in development of long-term control strategies, we examined in 2009 the range of diversity at the whole-plant and molecular level within and across six populations of S. molesta in Louisiana and Texas. Significant variation was observed for all five morphological traits measured both within and across collection sites. Root length was moderately associated with colony width, rhizome length, and leaf width when averaged across sites, but not when each location was evaluated separately. Cluster analysis revealed that S. molesta could be grouped into three to five distinct groups depending on the trait under consideration. Fruiting bodies (sporocarps) were observed only at one south Louisiana location. The salvinia weevil, Cyrtobagous salviniae Calder & Sands, was not found at any location during this study. Analysis of Molecular Variance of AFLP markers and DNA sequence analysis of the gapCp gene showed that the majority of molecular variation was detected within populations (87–93%) compared to diversity among populations (7–13%). Location (environment) was considered to be the most important source of variation for all measured traits. Principal Component Analysis (PCA) of AFLP and gapCp data revealed distinct clusters comprised of members across different collection sites. Although substantial morphological and molecular variations were detected both within and among populations, all data from this study suggested that these six populations were derived originally from the same clonal or related populations.