A Tale of Three Lineages: Expansion of Common Reed (Phragmites australis) in the U.S. Southwest and Gulf Coast

The common reed invasion in North America has spanned two centuries and is still ongoing. This expansion comprises two main forms: an introduced Eurasian lineage (identified here as “IntroducedPhragmites”) and a Gulf Coast lineage of unknown origin (identified here as “Gulf CoastPhragmites”). Both lineages are spreading beyond their current ranges and are colonizing Southwestern and Gulf Coast ecosystems where they have not previously existed. As a result, the native North American lineage of common reed (hereafter “nativePhragmites”) has declined in many places. The recent invasion of the U.S. Southwest by Introduced and Gulf CoastPhragmiteslineages has made this the only region in the world colonized by all three lineages. Along the central Gulf Coast where Gulf CoastPhragmitesremains the dominant form, IntroducedPhragmiteshas also recently invaded the Mississippi River delta. The consequences of these new invasions are uncertain, but a rapid response is needed to protect native species and ecosystems and reduce future control costs.