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Montana Field Guide

Montana Field Guides

Common Reed - Phragmites australis
Other Names:  Phragmites communis

Native/Exotic Species
(depends on location or taxa)

Global Rank: G5
State Rank: S4

Agency Status
MNPS Threat Rank:
C-value: 4

External Links

General Description
Cool season, rhizomatous perennial. Stems 1.5-3.5 m, forming dense stands. Leaves: blades 2–4 cm wide, flat and lax to ascending; sheaths with overlapping margins; ligules hairy, 3–6 mm long. Inflorescence a plumose panicle 15–32 cm long. Spikelets 11–14 mm long, with 3 to 8 florets, the florets covered by silky hairs from the rachilla; glumes shorter than the florets. Lemmas hairless, with an awn-like tip; the rachilla with long silky hairs; palea well developed. Disarticulation above the glumes; unit of dispersal the floret (Lavin in Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

In Montana, common reed consists of two subspecies (ssp.): ssp. americanus is native and more common while ssp. australis is introduced and very localized. Populations can be easily identified to the subspecies level (see diagnostic characteristics).

Diagnostic Characteristics
The MTNHP is tracking locations of common reed grass at the subspecies level. It is possible that both subspecies can be found adjacent to each other, yet be distinguishable.

Phragmites australis ssp. americanus is native and more common.
* Stem Color/Leaf Sheaths: Sheaths easily fall off, exposing the stem which will turn bright red when exposed to sunlight.
* Ligules: The width of the ligule membrane (not including the fringe of hairs at the top) is the critical measure. The ligule membrane is slightly wider, ranging from 0.4-1.0 mm tall.
* Glumes: In a spikelet, the first (or lowest) glume is relatively longer, ranging from 4-7 mm.
* Growth Form: It is less robust, typically reaching 6 feet (2 meters). It grows a bit more scattered, allowing for light to penetrate through the canopy and for other plants to colonize. Where nutrient availability is high, it will grow denser and taller. Stems break down easily over winter, allowing for other plants to grow.

Phragmites australis ssp. australis is exotic and less common (currently known to occur in Hill County).
* Stem Color/Leaf Sheaths: Sheaths cling tightly to stem, covering the dull, tan stem. It grows stolons, which are horizontal stems that spread on the soil surface.
* Ligules: The width of the ligule membrane (not including the fringe of hairs at the top) is the critical measure. The ligule membrane is slightly narrower, ranging from 0.1-0.4 mm tall.
* Glumes: In a spikelet, the first (or lowest) glume is relatively shorter, ranging from 2.6-4.2 mm.
* Growth Form: It forms dense monocultures, outcompeting native species. Stems can grow to 18 feet (6 meters). Where nutrient availability is high, it will grow denser and taller. Stems do not break down slowly, maintaining a thick thatch.

Sterile specimens of Phragmites are superficially similar to Arundo, a weedy, non-native species that gets as far north as Malheur County, OR. The genera can be distinguished when in flower because the glumes of Phragmites are glabrous whereas those of Arundo are covered with soft, whitish hairs 6-8 mm long. In addition, the glumes are much shorter than the lemmas in Phragmites.

Species Range

Range Comments
Phragmites australis is found on every continent except Antarctica and may have the widest distribution of any flowering plant (Tucker 1990). It is common in and near freshwater, brackish and alkaline wetlands in the temperate zones world-wide. It may also be found in some tropical wetlands but is absent from the Amazon Basin and central Africa. It is widespread in the United states, typically growing in marshes, swamps, fens, and prairie potholes, usually inhabiting the marsh-upland interface where it may form continuous belts (Roman et al. 1984).

Because Phragmites has invaded and formed near-monotypic stands in some North American wetlands only in recent decades there has been some debate as to whether it is indigenous to this continent or not. Convincing evidence that it was here long before European contact is now available from at least two sources. Niering and Warren (1977) found remains of Phragmites in cores of 3000 year old peat from tidal marshes in Connecticut. Identifiable Phragmites remains dating from 600 to 900 A.D. and constituting parts of a twined mat and other woven objects were found during archaeological investigations of Anasazi sites in southwestern Colorado (Kane & Gross 1986; Breternitz et al. 1986).

There is some suspicion that although the species itself is indigenous to North America, new, more invasive genotype(s) were introduced from the Old World (Metzler and Rosza 1987). Hauber et al. (1991) found that invasive Phragmites populations in the Mississippi River Delta differed genetically from a more stable population near New Orleans. They also examined populations elsewhere on the Gulf coast, from extreme southern Texas to the Florida panhandle, and found no genetic differences between those populations and the one near New Orleans (Hauber, pers. comm. 1992). This increased their suspicion that the invasive biotypes were introduced to the Delta from somewhere outside the Gulf relatively recently.

Phragmites is frequently regarded as an aggressive, unwanted invader in the East and Upper Midwest. It has also earned this reputation in the Mississippi River Delta of southern Louisiana, where over the last 50 years, it has displaced species that provided valuable forage for wildlife, particularly migratory waterfowl (Hauber 1991). In other parts of coastal Louisiana, however, it is feared that Phragmites is declining as a result of increasing saltwater intrusion in the brackish marshes it occupies. Phragmites is apparently decreasing in Texas as well due to invasion of its habitat by the alien grass Arundo donax (Poole, pers. comm. 1985). Similarly, Phragmites is present in the Pacific states but is not regarded as a problem there. In fact, throughout the western U.S. there is some concern over decreases in the species' habitat and losses of populations.

In Montana Phragmites australis populations are either the native ssp. americanus, which is more common, or the exotic ssp. australis, which is less common. The MTNHP is collecting data to track and map this species at the subspecies level.

Summary of Observations Submitted for Montana
Number of Observations: 7

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)


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Citation for data on this website:
Common Reed — Phragmites australis.  Montana Field Guide.  .  Retrieved on , from