Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Most plants grow their leaves a bit differently under water and above the water. Sometimes you cannot tell the difference, the difference is internal, but it affects whether the leaf can thrive and do its job (photosynthesis). I would try to set up a transition from water to air so the plant is not exposed just to air. Make the transition in a very humid place.
Here are a few ideas:
Put the plant stem in a pot of soil, but nip off any leaves that would have ended up under the soil.
Put the pot on a tray with some gravel.
Put some water in the gravel. It will evaporate and raise the humidity.
Put some sort of cover above the pot so it does not touch the leaves.
~A large plastic bag propped up with some sticks.
~A large glass jar
I know you said you are in a humid area, but even that might not be enough for a plant that started growing under water. I have several tanks with plants that grow mostly below the water, but eventually the stems are long enough that the plant is growing above the water but still under the lid. It is very humid under there. When I reposition the plant so it can grow out from under the lid I often see some unhappy edges of the leaves that are drying out a bit. And these are leaves that grew above the water, not under the water.