Fomitiporia ellipsoidea is a species of polypore fungus in the family Hymenochaetaceae, a specimen of which produced the largest fungal fruit body ever recorded. Found in China, the fruit bodies produced by the species are brown, woody basidiocarps that grow on dead wood, where the fungus feeds as a saprotroph. The basidiocarps are perennial, allowing them to grow very large under favourable circumstances. They are resupinate, measuring 30 centimetres (12 in) or more in length, though typically extending less than a centimetre from the surface of the wood. F. ellipsoidea produces distinct ellipsoidal spores, after which it is named, and unusual setae. These two features allow it to be readily differentiated microscopically from other, similar species. A number of chemical compounds have been isolated from the species, including several steroidal compounds. These may have pharmacological applications, but further research is needed.
First recorded in 2008 by Bao-Kai Cui and Yu-Cheng Dai in Fujian Province, it was revealed in 2011 that a very large fruit body, measuring up to 1,085 cm (427 in) in length, had been found by the pair on Hainan Island. The specimen, which was 20 years old, was estimated to weigh between 400 and 500 kilograms (880 and 1,100 lb). This was markedly larger than the previously largest recorded fruit body, a specimen of Rigidoporus ulmarius found in the United Kingdom, which had a circumference of 425 cm (167 in). The findings were formally published in September 2011, but attracted international attention from the mainstream press prior to this.