It's because of a process called osmosis. Land plants carry water from their roots to leaves while water plants undergo reverse osmosis and semi-permeability. Hard to explain but lemme give you some idea.
Well believe it or not, most if not all herbaceous perennial plants could survive with roots submerged in water. Some plants like photos, philodendrons, dracaenas, arums/aroids and spatiphyllums could survive with part of their leaves and stems submerged without rotting.
As much as most terrestial ferns appreciate lots of moisture/humidity, their roots must be well-drained. You could do a waterfall setup or a marsh setup with fern roots submerged but their leaves must be above water.
Bird's nest fern, boston ferns, maidenhair ferns can be planted around the water line but their roots must only be half-submerged. Running water and bright light usually takes care of them in the wild.
