Surprised to see these for sale

I was told as a child that you should never pick dandelions, as it makes you want the loo. I’m guessing it’s probably a diuretic and there’s a folklore rhyme about it, that I don’t know.

Its a "piss-en-lit".
"Wanting the loo" is a rather posh way of saying "wet the bed" but maybe you were posh.................once!!