Glyceria maxima is a perennial, semi-aquatic, rhizomatous grass. Stems are unbranched and can reach 2-8.2 ft. (0.6-2.5 m) in height.
Foliage
Leaves are 12-23.6 in. (30-60 cm) long, 0.2-0.8 in. (6-20 mm) wide, with an acute apex and a prominent midrib. The leaf margins have stiff, short hairs. The leaf sheaths are rough in texture with a reddish-brown band at the leaf junction.
Flowers
Flowering occurs from June through August, when flowers appear in 6-12 in. (15-30 cm) long open panicles. The panicle branches have short, stiff hairs like those on the leaf margins.
Fruit
The small seeds are 0.06-0.08 in. (1.5-2 mm) long, obovoid in shape and smooth in texture. This plant reproduces primarily vegetatively through rhizomes.
Ecological Threat
Glyceria maxima occurs in sunny to semi-shady wetlands, where it can form dense impenetrable monocultures that crowd out native species. It is native to northern Eurasia and was first found in North America in 1940 on the edge of Lake Ontario.