August 30, 2018 – Etienne Herrick, USGS Great Lakes Science Center
With invasive Phragmites australis now pervasive throughout the majority of the Great Lakes region, it can be tempting to tackle every stem you encounter. However, another subspecies of Phragmites – Phragmites australis subsp. americanus – is actually native to parts of the U.S. and Canada and is quickly losing territory, along with many of its wetland community neighbors, to the non-native counterpart. So, before you head outside with your Phragmites phighting gear, make sure the enemy you’re about to confront is indeed the non-native invasive, and not a poor native soul struggling to persist. To help you distinguish the native and invasive subspecies from one another, here are some identification tips:
Color
The photo on the left shows leaves from invasive (top) and native (bottom) Phragmites australis. The photo on the right highlights the red stems of native P. australis. Photo credit: Katherine Hollins.
In contrast to the yellowish leaves of native Phragmites, leaves of invasive Phragmites have a bluish hue. This difference is most notable when comparing the subspecies side by side. Furthermore, the stems of invasive Phragmites are typically a dull greenish-tan color, whereas native stems often display a reddish or purplish tone. However, invasive Phragmites produce stolons (spreading horizontal stems) that can at times also appear reddish.
Ligule Width
Important identifiers for native vs. invasive Phragmites can include leaf sheath, leaf blade, stalk, and ligule characteristics. Photo credit: University of Wisconsin Extension.
Ligule width is much narrower in invasive than in native Phragmites. Photo credit: Anton Reznicek, University of Michigan.
Native and invasive Phragmites have distinctive ligules – the membranous extension of the leaf sheath at the point where it meets the blade – making it a reliable indicator for identification. Invasive ligules are usually half as wide as those of native plants, measuring between 0.1 – 0.4 mm and 0.4 – 1.0 mm, respectively. When measuring this component, be sure not to include the fringe hairs at the top of the ligule.
Leaf Persistence
While the leaf sheaths of native Phragmites are easily removed and sometimes even fall off the stems, the sheaths of invasive Phragmites are particularly difficult to remove from dead stems.
Density
Left: A dense stand of senesced invasive Phragmites. Right: Sparse stems of native Phragmites grow alongside a variety of other species. Photo credit: Katherine Hollins and Wes Bickford.
Invasive Phragmites is often characterized by large, tall, and extremely dense monoculture stands that prevent sunlight from reaching other species and effectively crowds them out. The invasive stems break down slowly, further contributing to the appearance of exceptionally thick vegetation. Native Phragmites stands are far less robust, and usually appear as stems scattered throughout a relatively biodiverse wetland community.
Growing season
Due to its vigorous nature, invasive Phragmites has an extended growing season compared to the native subspecies. The invasive begins growing earlier in the year, and the native plants may have already gone dormant by the time the invasives begin senescing.
We hope these tips and tricks help you to effectively identify invasive Phragmites. Incorrect identification can lead to wasted time and resources, unnecessary pesticide application, and disruption of an otherwise healthy, highly biodiverse wetland community. Keep in mind that it is often best to use a combination of identification techniques to accurately determine which subspecies is present. If you are still unsure whether your Phragmites is native or invasive, genetic testing can provide you with a definitive answer and is available at both Oakland University in Rochester, MI, and at Utah State University in Logan, UT.
References and additional resources:
- Michigan Natural Features Inventory brochure- “Phragmites– Native or Not?”
- Great Lakes PhragmitesCollaborative page – “Native vs. Invasive?”
- Wisconsin Wetlands Association – “Invasive Plant Profile – Phragmites“
- US Department of Agriculture “Common Reed Plant Guide”
- National Park Service and US Fish and Wildlife Service “Plant Invaders of Mid-Atlantic Natural Areas” – pages 25-26
- Michigan DEQ and partners, “A Guide to the Control and Management of Invasive Phragmites”
- Ontario Phragmites Working Group Native vs. Invasive