Ask the cat.
Sorry, I just couldn't resist.
But seriously, all of the nettles that I am acquainted with have opposite leaves like your plant does.
Did you plant seeds for both catnip and nettle? Or did this just pop up in your garden?
Can you take a clear close-up photo of the stems?
To be on the safe side, until this plant is identified, please place a little wire cage around the plant to avoid accidental contact.
