The largest living being on earth is a mushroom: Armillaria ostoyae.
It covers a 890 hectares, most of its mass is underground and is therefore unknown. Its age is estimated between 2400 years and 8000 years.
By studying DNA samples taken from various locations of this colony, scientists realized that it was a single organism, genetically speaking: a huge super-organism as a host of genetically identical cells, the total biomass could rise up to 600 tons!
Scientists also believe it could achieve such size thanks to the humid climate of eastern Oregon.