Stuckenia vaginata

Stuckenia vaginata (syn. Potamogeton vaginatus), commonly called sheathed pondweed, big sheathed pondweed or large-sheathed pondweed is a water plant species that grows in fresh and brackish water in Europe, Northern Asia (excluding China) and North America. Sheathed pondweed is rare, but is not in the 2012 IUCN Red List. Stuckenia vaginata is a fully submerged aquatic plant and does not have any floating or emerged leaves. The flowers are wind pollinated and the seeds float. Tubers that are rich in starch are formed on the rhizomes. Reproduction can either be vegetative with tubers and plant fragments or sexual with seeds....read more on Wikipedia.