The "bananas" are storage tubers. The leaves of this particular water lily die back in winter and release the tubers to fall to the bottom of the pond where they winter over and then root down and sprout new leaves in spring.
Unfortunately the English language seems to be short of words (or imagination) so anything the English People encountered on their voyages of "discovery" they namend after something at home.
So we have tea-tree in NZ which is a Leptospermum, then we have tea-tree in Australia, which is a Melaleuca.
Both have been used by Captn Cook to brew something resembling Black Tea (which is Camellia sinensis) which they had run out of.
Then they found "pine-apples" which supposedly resemble a pine cone and do NOT grow on pine trees! The French called these "Ananas" which is what the locals called them, rather than inventing a new set of names.
Even plants that have already Latin names and Local names (where they come from) have to be named after something else: "NZ Yams" is a prime example. Nothing to do with yams which is a tropical climber, but related to Oxalis. The tubers are not even remotely similar-looking. The mind boggles...
And then we have "plums" in every country the English ever visited: Kaffir Plums, Burdekin Plums and hundreds more - all of which have nothing to do with a plum tree, which is a Prunus...
And so the storage tubers of some of these water lilies have inspired the name of "water banana"... go figure.
I HATE COMMON NAMES !!! :roll: :roll: :roll: