Reproductive dynamics and clonal structure in native and invasive subspecies of Phragmites australis

Background/Question/Methods

In North America, an introduced subspecies of Phragmites australis is aggressively invading wetlands and displacing the native subspecies. Generally thought to colonize areas with vegetative propagules, recent molecular studies suggest that seeds play an important role in dispersal and colonization. Research into the clonal diversity of P. australis shows that polyclonal stands are common, yet sampling regimes limit description and comparison of clonal architecture.  We sampled native and introduced P. australis stands in four Maine (US) salt marshes to compare the subspecies’ clonal diversity and structure using microsatellite markers. 

Results/Conclusions

Clonal architecture was found to vary by subspecies. The native stands were dominated by a single large clone, interspersed with single sample genotypes, while the introduced stands were relatively uniform with medium sized cohesive clones and fewer single sample genotypes.  A second survey compares the watershed-scale diversity of the two subspecies by sampling multiple stands in a marsh and found that all stands are polyclonal and no single clone is represented in more than one stand.  Our results and a systematic literature review indicate that P. australis stands may be more diverse than noted with some sampling methods, and reproduction by seed is more common than historically assumed, potentially affecting management of both native and introduced populations in North America.