Grifola frondosa is a wood-inhabiting fungus forming large annual fruitbodies at the trunk base of old living or dead trees. The species is mainly associated with Quercus spp. Except for veteran oak trees, its distinctive multipileate fruitbodies may occur on other old-growth deciduous hardwoods (Acer, Castanea, Fagus, Ulmus, etc.) and occasionally on large conifers. Grifola frondosa is a rarely recorded fungus throughout its range. Being confined to old and large trees, this species is under threat of declining primarily due to deforestation and uncontrolled logging in mature forests. In Europe, it is qualified as Near Threatened. At the global level the species is currently evaluated as Least Concern.

Fruit bodies of Grifola frondosa are morphologically similar all over its range. However, phylogenetic analysis has demonstrated a strong support for species partition separating eastern North American and Asian isolates and, based on a non-type European isolate, possible distinct European lineage (Shen et al., 2002). Still so far no taxonomic revision has been made to apply the name G. frondosa exclusively to the European lineage, or to separate the North American and Asian populations. Since the North American and Asian material is currently regarded as conspecific with the European records, this assessment is based on the overall species populations at a global scale.

Grifola frondosa is a lignicolous fungus confined to old and large trees, mainly oak but also other deciduous hardwoods or occasionally conifers. This conspicuous and rarely occurring fungus is declining globally due to deforestation, particularly large-scale logging of old-growth trees.

Grifola frondosa has a circumpolar range in the Northern hemisphere. In Europe, it is native to temperate hardwood regions, reaching up to the southern parts of boreal regions in Fennoscandia. In North America, it can be found throughout eastern, mid-western and southeastern states of the US as well as in Eastern Canada (Gilbertson, Ryvarden, 1986; Chen et al., 2000). In Asia, it is known to occur in southwestern and northeastern China and northeastern Japan (Yamanaka, 1997; Chen et al., 2000). A few records have been reported in Australasia: Australia and New Zealand (https://www.gbif.org/species/2540800, https://www.ala.org.au/, https://scd.landcareresearch.co.nz/Specimen/PDD_44884).

Grifola frondosa is a well-known species forming large and conspicuous fruit bodies that are usually searched for on old trees and hardly can be overlooked. Typically the fungus occurs at only one or a few trees per site (e.g. genetic distinct mycelial individuals).
The global population is estimated to exceed 20 000 mature individuals. Currently known population trends vary across its global range. Based on population decline, G. frondosa is nationally red-listed under threatened categories in over ten countries in Europe, while several countries reported its current population trends as stable. In North America, this fungus is presumably more widespread but there is no recent data on the population status of the species, therefore its population trends are unclear. In Asia, population status and trends are poorly known. However, at a global scale there is an evidence of continuing degradation of habitat quality, decline of old growth forests and loss of large old trees.

Grifola frondosa forms large fruit bodies on the ground at the trunk base of living and dying trees or dead trunks. It is known to cause white rot and butt rot of trees (Ryvarden, Gilbertson, 1993). Its long-lived mycelium may develop for many decades in decaying heartwood or in submerged rotting roots of old trees. It continues producing sporocarps at the base of dead trees and stumps. The species is confined to large old-growth trees.
Most frequently the fungus is found on Quercus spp. but may also occur on other hardwoods (Acer, Betula, Carpinus, Castanea, Eucalyptus, Fagus, Juglans, Nyssa, Populus, Ulmus) and occasionally on conifers (Pinus, Pseudotsuga, Larix) (Gilbertson, Ryvarden, 1986; Ryvarden, Melo, 2014). Records on conifers have been reported outside Europe: Pinus, Pseudotsuga, Larix – in North America (Gilbertson, Ryvarden, 1986), Abies – in China (Chen, 2002).
Grifola frondosa occurs in broadleaf temperate forests and hemiboreal broadleaf-coniferous forests. It prefers natural old-growth forests with minimum human impact but can be occasionally found under old individual trees in forest plantations.

The major threat is habitat destruction. Old growth forests are highly threatened worldwide, in particular large size trees are being cut down. Previously known and potential habitats are often destroyed by deforestation and excessive logging in mature forests. Inappropriate forest management, replacement of the forests dominated by slow-growing oak trees by fast-growing plantations result in habitat loss. Over-harvesting of wild edible mushrooms may be a threat. Re-establishment of the cultivated mycelia of non-native populations pose a potential threat to the environment.

Habitat conservation, sustainable forest management to enhance regeneration and continued growth of host trees are required. Since G. frondosa is widely cultivated and its strains of diverse geographic origin are maintained in various culture collections worldwide, they can be used in ex situ conservation.

Taxonomic research based on molecular studies including expanded sampling of isolates worldwide (European, Asian and North American) is required. Surveys are needed to study population trends and to monitor habitat trends.

Grifola frondosa is an edible mushroom. It is widely commercially cultivated and marketed, particularly in Asia and the US (Yamanaka, 1997; Chen et al., 2000). It is also considered to have medicinal values and is widely used in traditional Chinese medicine (Mizuno, Zhuang, 1995).

Chen, A.W., Stamets, P.E., Cooper, R.B., Huang, N.L., Han, S.-H. 2000. Ecology, morphology, and morphogenesis in nature of edible and medicinal mushroom Grifola frondosa (Dicks.: Fr.) S.F. Gray – Maitake (Aphyllophoromycetideae), International Journal of Medicinal Mushrooms, 2 (3): 221–228.
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Shen, Q., Geiser, D., Royse, D. 2002. Molecular phylogenetic analysis of Grifola frondosa (maitake) reveals a species partition separating eastern North American and Asian isolates. Mycologia, 94(3): 472–482. http://dx.doi.org/10.2307/3761781
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