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I am.pretty sure its family of sage! There are many species in this family you see. The flowers look a bit like clairy sage

Judith, I think it's Pontederia heart-shaped "Spoon River" (Pontederia cordata). Do you know this plant?

I have seen these waterplants yes. But the leves differ from the ones in your post....?

Yes. but the flowers are very similar. their several kinds. maybe it's some other kind of this plant?

Maybe! But i can tell you that you have got me really curious now