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

Few studies have examined population genetic variation in clonal, emergent, aquatic plant species. Phragmites australis (Cav.) Trin. ex Steudel is a c lonal, cosmopolitan species common to marshes, estuarine, and other wetland habitats. With the exception of several European studies examining local v ariation, little is known about the distribution of genetic variation in th is 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, ha s sparked interest in its ecology and genetic structure. In this study, ele ctrophoresis was used to analyze isozyme variation among 37 populations of P. australis from the eastern half of the U.S. The electrophoresis data str ongly support a primarily vegetative mode of reproduction and spread. A tot al of 21 multilocus, isozymic phenotypes were identified among the 37 popul ations. All populations sampled along the Gulf Coast (GC) from Texas to the Florida panhandle (with the exception of the two populations from the Miss issippi River delta) were uniform, sharing a single, multilocus phenotype. P. australis populations had lower levels of percent polymorphic loci and n umber of alleles per locus than typical asexual terrestrial species, but ha d a higher mean heterozygosity. Nei's genetic distance UPGMA depicts a subs tantial amount of geographic clustering of populations. However, population s described as 'invasive' showed no genetic similarity to one another. (C) 1999 Elsevier Science B.V. All rights reserved.