Phragmites is a robust erect perennial grass, aquatic or subaquatic, growing to 4 m in height (occasionally 6 m), strongly tufted, with an extensive rhizome system. It has rigid, many-noded stems and hollow internodes. Leaves alternate and are up to 70 cm long, with a ligule of hairs up to 1.5 mm long. Leaf blades are flat, up to 60 cm long and 8-60 mm wide.
Invasive vs. native
The invasive subspecies of phragmites (Phragmites australis) looks very similar to a native species (Phragmites americanus), and it is imperative that a stand be identified as invasive before implementing a management plan. When large-scale control is planned, any stands of native phragmites should be protected. Unlike the invasive strain, native phragmites rarely develops into monoculture stands, does not alter habitat, has limited impact on biodiversity, and does not deter wildlife. It can be difficult to tell native and invasive phragmites apart and genetic analysis may be necessary. Some identifying characteristics that may help tell the species apart are:
Invasive phragmites stands can grow up to 5 m tall (15 ft) in very dense stands with up to 200 stems per square metre. These near-monoculture stands can consist of 100% invasive phragmites. In comparison, native phragmites does not grow as tall and does not outcompete other native species, so there is more diversity within a stand (Phragmites BMP).
Invasive phragmites stems are generally tan or beige in colour, with blue-green leaves and large, dense seedheads. In contrast, native phragmites has reddish-brown stems, yellow-green leaves, and smaller, sparser seedheads.
Cross-breeding between invasive and native plants has not been confirmed in the field, but has been produced in laboratory studies. Where the plant is found in certain environmental conditions, such as those that occur along sandy coastal shorelines and deep water systems, the morphological differences described above are not definitive. If it is not clear whether a phragmites plant is invasive or native, it is recommended that an expert be consulted (Phragmites BMP).