Last week this weedful thing wasn't even up to my knee. Now it's shoulder-high (I'm 179 centimeters tall), and its weedful kin aren't far behind. I've no idea what it is (other than a weed) but it's growing where my sunflowers would be growing if they had bothered to pop out. That's a good strategy -- from small to tall in mere days. It's the tallest, thickest, and most vigorous entity in my garden!