invasive species gastropods physa acuta in a lake on a leaf of the invader pistia

alga algae animal aquatic plant plants araceae common duckweeds duckweed floating flora gastropods green background growth invader invasive species lake leaf leaves lemna turionifera lemnaceae natural nature nile cabbage physa acuta pistia stratiotes pistieae pond pool rootless seaweed shellflower southern ukraine spotless watermeal surface swamp tiny water lettuce wolffia