i found it in and near a pond. is it mentha aquatica? i just want to know it's not pennyroyal (and don't have much experience with growing anything) cause i read that its essential oils are toxic.
Welcome to Garden Web.
I suggest you asking at the forum linked below. Chances are that someone there can help you.
Here is a link that might be useful: Name that Plant Forum
Oops, I am not familiar with that too. I will research on it and get back to this thread. As for now I am not convinced that it is mentha aquatica because of the leaves surround it.