Antrodia labyrinthica is a wood-inhabiting fungus of old-growth submontane to montane forests in central and southern Europe. It is a rare species with a small population size estimated not to exceed 2,500 mature individuals, and its largest subpopulation is estimated to consist of fewer than 250 mature individuals. A population decline is inferred due to ongoing habitat loss and degradation, which will likely continue in the future. Therefore, the species is assessed as Endangered under criterion C2a(i) due to its small population size and continuing decline.

The species was formerly recorded under the name Antrodia variiformis in Europe, but that species is now known to only occur in North America. Antrodia kmetii, a recently described species (Vlasák et al. 2013), has been found to be a synonym of Antrodia labyrinthica, as they are molecularly identical (Vampola & Charvátová 2021).  Ryvarden et Melo (2017) transferred the species from Fomitopsis to Antrodia.

A rare European species, surviving in old-growth forests and virgin forests on decaying wood of conifers.

This species has been cited as occurring in seven countries: Italy, North Macedonia, Bosnia, Croatia, Slovakia, Spain, and France. The only known locality in Italy is located in the Riserva naturale Sasso Fratino (Bernicchia & Ryvarden 1996, Bernicchia 2007). The species has been recorded from Mt Korab in North Macedonia, Sutjeska National Park in Bosnia and Plitvice and Risnjak National Parks in Croatia (Tortić 1998, Karadelev & Rusevska 2016). It is known from ten localities in central Slovakia, including the Kremnica, Štiavnica and Vepor Mountains (Kunca et al. 2022). Ryvarden et Melo (2017) list the species from Spain and southern France but no specimen or locality data could be found to verify the occurrence of this species there.

This species was described in 1996 from a single locality in Italy (Riserva naturale Sasso Fratino) and is now known from about 16 localities across seven countries. It is typically only recorded from a few functional individuals (i.e. occupied fallen Abies trunks) per site, although it may fruit abundantly on its substrate (Tortić 1998). It is not known whether the fruiting bodies are annual or perennial, although they have been recorded throughout the year (Kunca et al. 2022). The species has been assessed as Critically Endangered on the national Red List for North Macedonia, where the species is only known from a single locality.
Given that the fruiting bodies of this species are typically large and conspicuous, and have been recorded throughout the year, along with the fact that polypores are generally well-known in Europe, it is thought that this species is genuinely rare. Further, this species appears to be an obligate of old-growth submontane to montane mixed forests (Kunca et al. 2022). Tortić (1998) considered the species to be an indicator of unmanaged, virgin fir forests, and all known occurrences are from old-growth forests with little to no anthropogenic impacts. Only an extremely small proportion of the original extent of old-growth mixed Abies forest remains within the range of this species. Brandrud (2019) estimated the decline of old-growth mixed Abies-Picea forest in Central-South Europe as approximately (10-)15-20% over the past 50 years. In Slovakia, where most of the records for this species originate, 1.58% of Abies and Picea woodland is classed as primary forest (Mikoláš et al. 2019). For these reasons, we conservatively estimate that there are no more than 150-200 unrecorded sites for this species. Field data suggests that only one to three fallen trunks are typically found with fruiting bodies per site, such that the number of functional individuals per site is estimated to be three. In lignicolous fungi which typically have few aggregated sporocarps per wood unit, each functional individual typically comprises about two mature individuals (Dahlberg & Mueller 2011). Thus, the total number of mature individuals is estimated as not exceeding 1,000 (900-1,200 using multipliers from Dahlberg & Mueller 2011). It is considered highly unlikely that there are more than 250 mature individuals in each subpopulation given the small number of mature individuals observed per site.

This species is a wood-inhabiting fungus which only occurs on fallen trunks of Abies alba in late-initial to intermediate stages of decay in old-growth mixed submontane to montane forest. Most records are from autumn, however Kunca et al. (2022) found fruiting bodies throughout the year. It is not known known if the fruiting bodies are perennial or annual. In Slovakia, the species has been recorded between 500 and 875 m asl (Kunca et al. 2022). It is not known if the species exhibits a preference for fallen trunks of certain diameter, although Tortić (1998) notes that sporocarps been observed on a wooden bench of Abies (i.e. a large trunk) and on small trunks.

Antrodia labyrinthica only occurs in old-growth forest and is intolerant of silvicultural activities such as logging, clear cutting, and removal of dead wood. Only a very small proportion of the original extent of potentially suitable habitat for this species remains in Central Europe, and much of it is located in small and isolated fragments (Sabatini 2018, Mikoláš et al. 2019). While much of the remaining area of old growth mixed Abies forest is protected, threats such as removal of dead wood following storms or pest outbreaks (i.e. salvage cutting) and lack of regeneration due to ungulate grazing continue to lead to a decline in the quality of habitat for this species, even in protected areas (Brandrud 2019, Mikoláš et al. 2019, Kunca pers. comm. 2023). Formerly managed forests in Central Europe have been found to still contain less downed wood than a pristine forest 220 years after the cessation of anthropogenic disturbance, highlighting the importance of protecting remaining stands of primary forest for retaining suitable habitat for A. labyrinthica (Albrich et al. 2021).
A. labyrinthica has only been recorded from fallen logs of Abies alba (Silver fir). While A. alba is assessed as Least Concern on the Red List (Farjon 2017), several factors including overgrazing, unsustainable forestry practices, and an increase in the frequency of droughts and pathogen events due to climate change have been cited as contributing to a decline in this tree species (Bledy et al. 2024). Because fir is particularly palatable to ungulates, wood-inhabiting fungi such as A. labyirinthica which are strict fir specialists are especially vulnerable to overgrazing pressure (Holec & Kučera 2020).

Protection of remaining old-growth submontate to montane mixed forests is needed for ensuring the continued existence of this species, which does not occur in managed forests. In particular, leaving dead wood in protected old growth forests is critical for ensuring appropriate substrate for this species remains. Reducing ungulate grazing pressure in old growth forests, for example with fencing, may help maintain long-term habitat quality by improving regeneration potential of Silver fir.

No uses have been recorded.

RYVARDEN L., MELO I. (2014): Poroid fungi of Europe. – Synopsis Fungorum 31. Fungiflora, Oslo.