Description from Flora of China
Perennial reeds, rhizomatous. Culms tall, erect, leafy, hollow. Leaf blades all cauline, broadly linear, base rounded, deciduous; ligule membranous with ciliate margin. Inflorescence a large, plumose, copiously branched panicle with numerous, crowded, silky-hairy spikelets. Spikelets laterally compressed, with several loosely arranged florets, lowest floret masculine or empty, resembling glumes but longer, persistent, succeeding florets bisexual, rachilla disarticulating between bisexual florets; glumes shorter than lemmas, unequal, papery, 3–5-veined; floret callus linear, silky-plumose with long spreading hairs; lemmas of bisexual florets very narrow, hyaline, 1–3-veined, glabrous, entire, long caudate; palea short, hyaline. Stamens 2 or 3.
This is a genus of tall, aquatic or semiaquatic reeds found in nearly all parts of the world. The species are very variable, closely related, and indistinctly separated. Liu (Phragmites Resources, 1989) recognized five varieties in Phragmites japonicus, five varieties in P. karka, and 74 varieties in P. australis!
Arundo and Neyraudia have a similarly tall, reedy habit and plumose panicle, but both differ from Phragmites in the spikelet hairs arising on the lemmas and not on the floret callus. Neyraudia is further distinguished by its solid culms. Arundo generally has broader leaves cordate at the junction with the sheath.
Phragmites reeds provide a source of fiber, the rhizomes have medicinal uses, and the plants also aid soil retention. Reed beds can also be used for the purification of water.
Four or five species: cosmopolitan; three species in China.