[quote="Gelert"]The other thing nettles have is oxalic acid (i.e. the stingy compound) which chelates metal cations like its going out of fashion. You end up with calcium oxalate when they react, or the stuff in kidney stones. Think on about the absorption kinetics of them!
Drat, large amounts of oxalic acid is what makes spinach so useless as a calcium source. If I may ask, how do you know nettles have oxalic acid? At least via google I haven't been able to find any measurements about anything from a reliable source.