Phellinus ellipsoideus (formerly 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.

This was markedly larger than the previously largest recorded fungal fruit body, a specimen of Rigidoporus ulmarius found in the United Kingdom that had a circumference of 425 cm (167 in).

[1] Five specimens of the then-unknown species were collected during field work in the Wanmulin Nature Reserve (27°03′N 118°08′E / 27.050°N 118.133°E / 27.050; 118.133), Jian'ou, Fujian Province.

[3] Phylogenetic analysis of large subunit and internal transcribed spacer DNA sequence data, the results of which were published in 2012, concluded that the species then known as F. ellipsoidea was closely related to Phellinus gabonensis, P. caribaeo-quercicolus and the newly described P. castanopsidis.

[4] While the taxonomic database Index Fungorum follows the 2012 study, MycoBank continues to list Fomitiporia ellipsoidea as the correct binomial.

[2] The original description characterized them as measuring up to 30 centimetres (12 in) "or more" in length,[7] 20 cm (7.9 in) in width, and extending 8 mm (0.3 in) from the wood on which they grow at their thickest point.

The shiny surface of the hymenium, the spore-producing section of the fruit body, is covered in pores and ranges in colour from yellow-brown to rust-brown.

[10] The main structure of the fruit body consists primarily of an agglutination (mass) of interwoven skeletal hyphae, which are golden- to rust-brown.

[13] Five species of Fomitiporia, F. bannaensis, F. pseudopunctata, F. sonorae, F. sublaevigata and F. tenuis, share with P. ellipsoideus the resupinate fruit bodies and the setae in the hymenium.

[16] In 2010, Cui and Dai were performing field work in tropical woodland on Hainan Island, China, studying wood-rotting fungi.

[18] They were initially unable to identify the specimen as P. ellipsoideus, because of its large size, but tests revealed its identity after samples were taken for analysis.

[9] After their initial encounter with the large fruit body, Cui and Dai returned to it on two subsequent occasions, so that they could study it further.

[9] Nicholas P. Money, executive editor of Fungal Biology, in which the findings were published, praised the pair for not removing the fruit body, thereby allowing it "to continue its business and to marvel visitors to Hainan Island".

[18] The discovery was formally published in Fungal Biology in September 2011,[15] but gained attention in the mainstream press worldwide prior to this.

[21] Prior to this discovery, the largest recorded fruit body of any fungus was a specimen of Rigidoporus ulmarius, found in Kew Gardens, United Kingdom.

In 2003, a large specimen of A. solidipes (synonymous with A. ostoyae) was recorded in the Blue Mountains, Oregon, covering an area of 965 hectares (2,380 acres).

Prior to this, an A. gallica (synonymous with A. bulbosa) organism was the largest recorded, covering 15 hectares (37 acres), weighing approximately 9,700 kilograms (21,400 lb).

[22] In 2011, research into the chemistry of P. ellipsoideus was published in the journal Mycosystema by Cui, along with Hai-Ying Bao and Bao-Kai Liu of the Jilin Agricultural University.

[25] Steroidal compounds, like those isolated from P. ellipsoideus, can have pharmacological applications; for instance, some can act as anti-inflammatories (including ergosterol) or inhibit tumour growth.

The 2011 study concluded that, as P. ellipsoideus contained a large number of diverse steroidal compounds, there may be comparatively high pharmacological activity in the fungus; however, more research would be needed to confirm this.

[24] Research published in 2012 named fomitiporiaester A, a natural furan derivative isolated from methanolic extract of P. ellipsoideus fruit bodies.