Probably Venus' Looking Glass, Triodanis perfoliata. I think it is an annual. It is native, but most people pull it out...not good or bad, depending on what you want. All plants take up space, water, and nutrients, so if you have too many, other plants will have to "share."

great, thanks, I dont mind having it around, as long as it is not poisonous to people, dogs or other plants