Isozyme variation among populations of the clonal species, Phragmites australis (Cav.) Trin. ex Steudel

Abstract

Few studies have examined population genetic variation in clonal, emergent, aquatic plant species. Phragmites australis (Cav.) Trin. ex Steudel is a clonal, cosmopolitan species common to marshes, estuarine, and other wetland habitats. With the exception of several European studies examining local variation, little is known about the distribution of genetic variation in this taxon, particularly in the U.S. In recent years, the rapid and invasive, vegetative spread of P. australis into disturbed marsh habitats in the U.S., particularly on the Eastern Seaboard and the Mississippi River delta, has sparked interest in its ecology and genetic structure. In this study, electrophoresis was used to analyze isozyme variation among 37 populations of P. australis from the eastern half of the U.S. The electrophoresis data strongly support a primarily vegetative mode of reproduction and spread. A total of 21 multilocus, isozymic phenotypes were identified among the 37 populations. All populations sampled along the Gulf Coast (GC) from Texas to the Florida panhandle (with the exception of the two populations from the Mississippi River delta) were uniform, sharing a single, multilocus phenotype. P. australis populations had lower levels of percent polymorphic loci and number of alleles per locus than typical asexual terrestrial species, but had a higher mean heterozygosity. Nei's genetic distance UPGMA depicts a substantial amount of geographic clustering of populations. However, populations described as `invasive' showed no genetic similarity to one another.