Some aquatic plants float on the water’s surface or have a few leaves sticking out of the water. These leaves have stomata and collect carbon dioxide, like terrestrial plants.
I have seen on your other post that it is hard to get carbon dioxide in the water. I wonder how plants get a lot of it?
Some plants stick their leaves out of the water to get carbon dioxide. Carbon dioxide molecules must first pass the air and water barrier to dissolve in water. Once CO2 crosses the water’s surface, the molecules gain a shell of water molecules and transfer from carbon dioxide gas. That is why it is a bit slow.