The largest organism is a fungus
A single honey fungus in Oregon, Armillaria ostoyae, occupies on the order of ten square kilometres of forest floor.
Armillaria spreads as rhizomorphs and as a mat of mycelium, and it fruits, occasionally, as honey-coloured mushrooms. Genetic sampling in the Malheur National Forest found one individual extending across roughly 2,200 acres, something near nine square kilometres, with an age estimated in the thousands of years.
Size here means area of one genetic individual. By that measure the fungus beats every animal. Clonal plants, including some aspen groves, are the serious rivals, and a different Armillaria in Michigan is another claimant. 'Largest' depends on the ruler. The Oregon fungus is enormous on every ruler that has been applied to it.
Caveats
- The outline is inferred from samples, not from excavating the whole organism.
- Age estimates are rough. The area is the better-measured claim.
Sources
- 1Ferguson B. A. et al.. Coarse-scale population structure of pathogenic Armillaria species in a mixed-conifer forest. Canadian Journal of Forest Research 33, 2003.