Fanwort & Hornwort
Fanwort
Fanwort is a fully aquatic true plant. It grows steadily through the warm months, and can choke-out large areas, then dies back in the winter. Fanwort produces tiny flowers above the surface.
-- Wikipedia
Hornwort
Hornwort is very similar to Fanwort. In fact, unless you are a botanist, it might as well be the same thing. Hornwort produces tiny flowers underwater, an easy way to tell them apart.
-- Wikipedia
Fanwort is the more common of the two, if you are paying attention. Both grow almost to the surface, but are not usually a problem for paddling. As with Water Lilies, I have tried to take Fanwort for the aquarium, but it just dies. My guess is it needs full sun and nothing less will do.