The biology of Canadian weeds. 129. Phragmites australis (Cav.) Trin. ex Steud.

Abstract

Phragmites australis (Cav.) Trin. ex Steud.-common reed, is a perennial, emergent aquatic plant with annual cane-like stems developed from an extensive rhizome system. It grows in low-lying wet areas such as fresh and salt-water marshes, drainage ditches, shallow lake edges, sandy banks, roadsides, woodlands and rocky places. Stems can reach up to 6.0 m in height, vary in diameter from 4 to10 mm and have 10 to 25 cm long hollow internodes. Clones are extended by perennial rhizomes with extensive aerenchymatous tissue that supplies oxygen. Roots develop from rhizomes and other submerged parts of shoots. Leaves are smooth, alternate with narrow-lanceolate laminae, 20 to 70 cm long and 1 to 5 cm broad, and tapering to long slender points. The inflorescence is a terminal panicle, often 30 cm long, dull purple to yellow, with main branches bearing many spikelets. Seed production and germination are extremely variable and comparatively rare in many populations. Phragmites australis carries out photosynthesis through the C3 pathway (or a variation thereof). Studies of genetic variation through isozyme and other molecular methods suggest that the populations are very closely related, and that variation in the metapopulation is small. Chloroplast DNA sequences of two non-coding regions indicate that non-native introduced genotypes of P. australis have displaced native genotypes in parts of North America. Phragmites australis often forms extensive monocultures in North America. As a consequence, habitat quality and species diversity have been documented to decline. However, in roadside populations it is effective in taking up many typical heavy metals that originate from nearby highways and buildings. Phragmites australis is found in all Canadian provinces and the Northwest Territories, but not in the Yukon Territory or Nunavut. The infestation of P. australis is most severe in the Great Lakes region and its migration is primarily mediated through rivers, canals and waterways but roadways are increasingly becoming important. Changes in the water regime have been linked to its success and could ultimately result in changes to the floristic composition of a habitat. Rodeo™, an aqueous solution of the isopropylamine salt of glyphosate, is most frequently used to control P. australis populations. Other methods of control include cutting, burning, and drainage of the species’ habitat. As P. australis is considered to be invasive in North America, introduction of biological control agents is now being investigated. Key words: Phragmites australis; common reed; Canadian distribution; wetlands; invasive weed