Willow grows wonderfully in water. Just put a stick in, there will grow
roots underwater and leafs above. I put a big one in my garden
pond, to make it clean the water, give some shade and look pretty. I tied it to rocks with a string, like a boat. Today I cleaned the
pond edge and looks like the willow survived winter (although some parts of it died).
Then a strong wind blew more willow twigs to my garden, so I took one and put it in my aquarium. It started really quickly and even produced a flower! I don't have a picture because it's hidden behind another plant but looks lovely.
Here is a picture of my aquarium - it's not really "just water" as it has garden soil on the bottom (look up Diana Walstad - she wrote a book about this type of low tech aquarium). I took soil from mole mound and covered it with gravel. It's a year old now.
The willow is to the right, and the sushi box under one lamp has tomato seeds sprouting in it!