Largest described fruiting body: estimated at 400–500 kg

In 2011 Yu-Cheng Dai and Bao-Kai Cui described in Fungal Biology a fruiting body of the bracket fungus Fomitiporia ellipsoidea found on Hainan Island in southern China. They estimated its volume at 409,000–525,000 cubic centimetres, its weight at 400–500 kilograms and its age at about twenty years. It was the first documented fungal fruiting body of that size, by both volume and weight.

That scale is possible because brackets in the genus Fomitiporia are perennial. A bolete cap grows and collapses within a fortnight — a bracket adds a fresh layer of tubes each year and leaves the old layer underneath. The Hainan record is therefore not one extraordinary season of growth but two decades of a mycelium in dead wood laying down material at a steady rate.

Two different records get mixed together in popular lists, and they are worth separating. A fruiting body is a reproductive organ — the specific visible structure. The organism is the whole mycelium, and the largest one known belongs to a honey fungus in Oregon that covers hundreds of hectares. The Hainan fungus holds the first record, the honey fungus the second. Comparing them is like comparing a single fruit with an entire orchard.

The measurement has limits, and the authors state them. Volume was computed from external dimensions, and weight estimated from the density of the material rather than by weighing the whole thing in the field. Hence a range rather than a single figure. Age was reconstructed from the number of hymenial layers, the standard method for perennial brackets, but it assumes one layer per season. That assumption usually holds and is never quite exact.

What the evidence actually shows

This record concerns one fruiting body, not the entire fungal individual. The perennial, resupinate polypore grew beneath a fallen trunk in forest on Hainan Island. It reached 10.85 m long, 82–88 cm wide, and 4.6–5.5 cm thick. The authors calculated a volume of 409,000–525,000 cm³ and multiplied it by the mean fresh density of three samples. The resulting 400–500 kg is therefore an estimate, not the weight of the whole structure placed on a scale. About 20 years of age was inferred from growth layers. The fruiting body was left in place; sampled tissue and a culture were deposited, and an ITS sequence supported its identification as Fomitiporia ellipsoidea (also encountered in the later combination Phellinus ellipsoideus). It does not compete with Armillaria for largest genet: one comparison concerns a reproductive structure, the other an extensive mycelial individual.