High Quality Content by WIKIPEDIA articles! Glyceria maxima (Hartm.) Holmb. (syn. G. aquatica (L.) Wahlenb.; G. spectabilis Mert. W.D.J. Koch; Molinia maxima Hartm.; Poa aquatica L.; Reed Mannagrass; Reed Sweetgrass) is a species of rhizomatous perennial grasses in the mannagrass genus native to Europe and Western Siberia and growing in wet areas such as riverbanks and ponds. It is highly competitive and invasive and is often considered noxious weed outside its native range.