Among the contenders for the world’s largest living organism is something usually considered much smaller than a blue whale, or a towering sequoia. This particular organism is so big, one needs an aerial map to grasp its size, and even then it’s not completely visible as most of it is underground. It’s a specimen of the fungus Armillaria ostoyae, first discovered two decades ago though thought to be a few millennia old by then, and so large it is spread over nearly four square miles – a space equivalent to one-sixth of Manhattan, or nearly 8,300 Olympic-sized swimming pools – and weighs as much as three blue whales combined.