Urtica gracilis (often classified as a subspecies of stinging nettle,Urtica dioica subsp. gracilis) is a widespread nettle species in North America including Canada and Alaska. It has many local names including slender nettle, California nettle and American nettle. This year, my tallest nettle is currently over 2.9m high!
Added 300917: The friend in Granville, Ohio who sent me the seed of this nettle writes: “I collected the Urtica gracilis along the back of my property, near an old railroad (now a bike trail). It’s a common plant in “waste places”. I’ve never seen the plants grow that large here. Could your additional sunlight be to blame?”