Originally from Eurasia, exotic Phragmites australis ssp. australis (Figure 1) invades high quality and disturbed wetlands alike, reducing biodiversity by excluding other plant life and disrupting ecological function. It’s spread has been rapid, and land managers are hard-pressed to keep up.
Figure 1. Phragmites australis ssp. australis
Native Phragmites australis ssp. americanus has co-evolved with other native flora and fauna, has existed in Illinois for thousands of years, and does not typically reduce biodiversity or cause ecological disruption where it occurs. It most often forms either loose or localized colonies, which allow for the co-occurrence of other species. The growth form of native Phragmites lends a unique element of physical structure to wetlands and the tissues of the plant support a number of insect species.
For these reasons, resources need to be directed towards the eradication of the exotic subspecies and not wasted eradicating stands of the native subspecies. The eradication of native Phragmites may simplify wetland food webs and the associated disturbance may create opportunities for truly harmful invaders.
Identification of native and exotic subspecies isn’t especially difficult, if you know what to look for. Here I focus on characteristics most easily observed during the fall and winter. Fall and winter are arguably the best time to identify the native and exotic subspecies, because some of the most reliable characteristics for identification are most clearly observed on dormant plants.
Investigation of several characteristics is strongly advised, because interpretations of certain more qualitative characteristics can vary from person to person, and some plants may be ambiguous or atypical with respect to any single characteristic. Hybrids between native and exotic subspecies would be problematic for identification, but hybrids are exceedingly rare.
Read more for a precise comparison of the two subspecies.