there is a poem that goes "remember friend as you pass by that you are now what once was I, as i am now what you must be, prepare for death and follow me."
OBJECTION!!!!! "Miles" is a linear measurement and "Acres" is a quadratic measurement. However, the "large-ness" of an organism should be measured cubically, in volume. Secondly, the fungus has tiny, very thin, rootlike structures that do not take up all of the space underground, so given this data, it cannot conclusively be said to be the largest organism.