Is there such a thing as an amphibian plant?

The plant has structures called stoma that regulate water/gas exchange. Also you have to remember that plants remove CO2 from the atmosphere and release oxygen. So for them to be able to live strictly in water they have to have a mechanism for removing CO2 that does not involve the stoma - how do underwater plants do it? Algae? I know I am asking more questions than I am answering, but maybe it might help in the fleshing out of your story.