Elodea, also known as Canadian pondweed, is a common aquarium and pond plant, and it’s a master of regrowing from fragments. In some regions, only female plants exist, so it spreads almost entirely by broken pieces. Fragments, even from a single node, can float away on the water, or hitch a ride on a boat, a fishing net or even a duck, and then root downstream. Related plants like hydrilla spread in a similar way.