Phellinus ellipsoideus
Phellinus ellipsoideus is a species of wood-decaying polypore fungus in the family Hymenochaetaceae, native to southern China, where it grows as a saprotroph on dead hardwood trees, primarily fallen wood of oaks in the subgenus Cyclobalanopsis, in tropical and subtropical forests. It is best known for producing exceptionally large perennial fruiting bodies, with the record specimen discovered on Hainan Island measuring 10.85 m in length, 82–88 cm in width, and 4.6–5.5 cm in thickness, estimating a volume of 409,000–525,000 cm³ and a fresh weight of 400–500 kg after 20 years of growth.[1] Originally described as Fomitiporia ellipsoidea in 2008 from specimens collected in Fujian Province (Cui & Dai, Mycotaxon 105: 341–350), the species features a dimitic hyphal system, hooked hymenial setae, and ovoid to broadly ellipsoid basidiospores that are colorless, thick-walled, weakly dextrinoid, and moderately cyanophilous. In 2013, phylogenetic analyses of LSU and ITS rDNA sequences led to its transfer to the genus Phellinus (Cui et al., Mycol. Progress 12: 341–351), where it forms a monophyletic clade with species such as P. gabonensis and P. caribaeo-quercicolus, aligning more closely with the P. igniarius group than with Fomitiporia. Basidiocarps are typically resupinate to pileate, imbricate, and woody-hard, with a brown upper surface, angular pores (3–4 per mm), and a thick context up to 20 mm. Ecologically, P. ellipsoideus contributes to wood decomposition in its native range, primarily in provinces like Hainan and Fujian, though its distribution may extend to other parts of southern China.[1] The fungus's ability to form massive, long-lived fruiting bodies highlights its adaptation to stable, humid tropical environments, and its discovery has advanced understanding of fungal size limits and growth strategies in Basidiomycota.[1] Limited research has explored its potential medicinal properties, including isolation of an antitumor furan derivative from its fruit bodies in 2012, but no widespread traditional or economic uses are documented.[2] Its taxonomic revisions underscore ongoing refinements in hymenochaetoid fungal classification through integrated morphological and molecular approaches.Taxonomy and phylogeny
Classification history
Phellinus ellipsoideus was originally described as Fomitiporia ellipsoidea by Bao-Kai Cui and Yu-Cheng Dai in 2008, based on specimens collected from the Wanmulin Nature Reserve in Fujian Province, eastern China. The species was characterized by its perennial, woody basidiocarps and ellipsoidal basidiospores, with the type specimen (holotype Cui 4270) deposited at the herbarium of the Institute of Microbiology, Beijing Forestry University (BJFC). This description was published in Mycotaxon 105: 341–350 as part of a series on wood-rotting fungi in eastern China.[3] In 2013, following molecular phylogenetic analyses using rDNA sequences (ITS and nuclear LSU regions), the species was transferred to the genus Phellinus as Phellinus ellipsoideus by Bao-Kai Cui, Yu-Cheng Dai, and Cony Decock. This reclassification was prompted by evidence that Fomitiporia ellipsoidea clustered within the Phellinus clade, distinct from the type species of Fomitiporia, leading to a broader revision of generic boundaries in the Hymenochaetaceae. The transfer was formally proposed on page 348 of a study published in Mycological Progress, which also described a new species, Phellinus castanopsidis, and provided preliminary phylogenetic insights into poroid Hymenochaetaceae from southern China.[4] Currently, P. ellipsoideus is classified in the Kingdom Fungi, Phylum Basidiomycota, Class Agaricomycetes, Order Hymenochaetales, Family Hymenochaetaceae, and Genus Phellinus. This placement reflects ongoing taxonomic refinements in the family based on molecular data, with no further synonyms or reclassifications reported since 2013.[4]Phylogenetic position
Phellinus ellipsoideus is positioned within the core Phellinus clade of the Hymenochaetaceae family, as determined by multi-locus phylogenetic analyses incorporating the internal transcribed spacer (ITS) and nuclear large subunit ribosomal DNA (nLSU) regions, with later studies including additional loci such as translation elongation factor 1-α (EF1-α) and RNA polymerase II subunit 2 (RPB2). These analyses reveal its close phylogenetic affinity to other East Asian species in the genus, particularly forming a distinct group allied with the P. igniarius complex, supported by high bootstrap values in maximum likelihood trees (98–100%).[5][6] The species was originally described as Fomitiporia ellipsoidea in 2008 but was reclassified to Phellinus in 2013 based on combined morphological traits, such as the presence of setal hyphae and dimitic hyphal structure, and genetic divergences in rDNA sequences that place it outside the Fomitiporia clade. This distinction is evidenced by phylogenetic trees showing Fomitiporia species clustering separately with stronger support for Phellinus placement (posterior probability 1.0).[7] Within the broader Hymenochaetaceae family tree, P. ellipsoideus occupies a position among the wood-decaying polypores, contributing to the genus Phellinus as a representative of East Asian biodiversity in poroid hymenochaetoid fungi. Recent studies on family diversity, utilizing expanded ITS and nLSU datasets, reinforce this 2013 reclassification and highlight its stable placement in monophyletic analyses.[6][8]Morphology and identification
Macroscopic features
The basidiocarps of Phellinus ellipsoideus are perennial, typically resupinate to pileate and imbricate, developing a woody-hard consistency when dry. They have a thick context up to 20 mm and usually measure up to 30 cm in length and less than 2 cm in thickness. These fruit bodies form on the undersides of large fallen trunks, often creating extended, continuous pulvinate sheets that adhere closely to the substrate.[9] The upper surface appears dark brown to blackish, with a crust-like texture interrupted by faint zonation lines marking annual growth. The margin remains sterile and whitish during active growth, while the pore surface is cream to buff, featuring angular pores numbering 3–4 per mm and tubes extending 1–2 mm in length.[9] This species exhibits a growth habit on dead angiosperm wood in subtropical forests, where it produces extensive crust-like patches or small, shelf-like brackets that contribute to wood decomposition. Under optimal conditions, individual basidiocarps can exceptionally reach massive sizes, such as the record specimen measuring 10.85 m in length, 82–88 cm in width, and 4.6–5.5 cm in thickness, with an estimated fresh weight of 400–500 kg.[1]Microscopic features
The microscopic features of Phellinus ellipsoideus provide key diagnostic traits for species identification under the microscope. Basidiospores are ovoid to broadly ellipsoid, hyaline, thick-walled, weakly dextrinoid, and moderately cyanophilous, with dimensions of 4.5–5.5 × 4–4.5 µm. The hyphal system is dimitic, comprising generative hyphae that are 2–4 µm in diameter and bear clamp connections, alongside thick-walled, non-septate skeletal hyphae. Basidia are club-shaped, measuring 12–18 × 4–6 µm, and typically produce four sterigmata, with hooked setae present in the hymenium. No cystidia are observed, and the context appears golden brown in color.[9]Similar species
Phellinus ellipsoideus is morphologically similar to other members of the Hymenochaetaceae family, particularly those with resupinate or crust-like fruit bodies on hardwood hosts, but can be distinguished by its combination of pore size, spore dimensions, hyphal characteristics, and host specificity. A notable relative is Phellinus linteus, which exhibits a comparable brown, crustose appearance but features smaller pores (6–8 per mm) and typically grows on broadleaf trees such as mulberry or oak rather than the tropical hardwoods preferred by P. ellipsoideus.[10] P. ellipsoideus can be differentiated from Fomitiporia robusta by spore size and the presence of hooked setae; F. robusta has larger spores (5–7 × 4–5 µm) and lacks these distinctive hooked structures in the hymenium. In contrast, species like Inonotus obliquus produce sterile sclerotia forming irregular, black conks without a fertile pore surface, whereas P. ellipsoideus develops resupinate, fertile fruit bodies with a distinct poroid underside.[11]| Feature | Phellinus ellipsoideus | Phellinus linteus | Fomitiporia robusta | Inonotus obliquus |
|---|---|---|---|---|
| Spore size (µm) | 4.5–5.5 × 4–4.5 | 5–6 × 4–5 | 5–7 × 4–5 | 6.5–8 × 5–6.5 |
| Hyphal system | Dimitic with hooked setae | Dimitic | Dimitic, no hooked setae | Monomitic |
| Host preferences | Tropical hardwoods (e.g., Ficus) | Broadleaf trees (e.g., oak) | Deciduous hardwoods (e.g., Quercus) | Birch (Betula) |