Phragmites australis, known as the common reed, is a species of flowering plant in the grass family Poaceae.

Where conditions are suitable it can also spread at 5 metres (16 feet) or more per year by horizontal runners, which put down roots at regular intervals.

[citation needed] It can grow in damp ground, in standing water up to 1 m (3 ft 3 in) or so deep, or even as a floating mat.

[1] The flowers are produced in late summer in a dense, dark purple panicle, about 15–40 cm (6–15+1⁄2 in) long.

Recent studies have characterized morphological distinctions between the introduced and native stands of Phragmites australis in North America.

[2] It is a helophyte (aquatic plant), especially common in alkaline habitats, and it also tolerates brackish water,[4] and so is often found at the upper edges of estuaries and on other wetlands (such as grazing marsh) which are occasionally inundated by the sea.

A study demonstrated that P. australis has similar greenhouse gas emissions to native Spartina alterniflora.

In Europe, common reed is rarely invasive, except in damp grasslands where traditional grazing has been abandoned.

[7] However, there is evidence of the existence of Phragmites as a native plant in North America long before European colonization of the continent.

[15] While typically considered a noxious weed, in Louisiana the reed beds are considered critical to the stability of the shorelines of wetland areas and waterways of the Mississippi River Delta, and the die-off of reed beds is believed to accelerate coastal erosion.