Some photos of spherical water droplets on Salvinia floating plant.
I think Salvinia is one of the easiest floating plant to keep in an aquarium. It has 3 forms Primary form, Secondary form, and Tertiary form and will adopt the most suitable form for whatever conditions is in your aquarium. (The photos shown below are Primary form. Initially, when I bought it, it was in Tertiary form.)
Mathtuition88 