Butomus umbellatus

Butomus umbellatus is a Eurasian plant species in the family Butomaceae. It is the only species in the family. Common names include flowering rush or grass rush. Introduced into North America as an ornamental plant it has now become a serious invasive weed in the Great Lakes area and in parts of the Pacific Northwest. In Israel, one of its native countries, it is an endangered species due to the habitat loss. It can also be found in Great Britain locally, for example at the Caldicot and Wentloog Levels. The plant is a rhizomatous, hairless, perennial aquatic plant. Its name is derived from Greek bous, meaning "cow", "ox" etc. and tome, a cut (the verb 'temnein' meaning "to cut"), which refers to the plant's swordlike leaves....read more on Wikipedia.