Assessment Notes

Justification

Squamanita paradoxa is a biotrophic fungus with extreme host specificity, that parasites the closely related saprotroph Cystoderma amianthinum. Whilst widespread in Europe and North America, it seems globally rare, though seen more frequently in Europe than in North America. Its host, however, is widespread and common, with no evidence of decline. Therefore, the species is assessed as Least Concern (LC).

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Geographic range

Squamanita paradoxa's known distribution spans Europe and North America (GBIF 2024).

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Population and Trends

It is globally rare, though seen in Europe slightly more frequently than in North America. Its host is widespread and common, with no evidence of decline. Occasionally, Squamanita paradoxa is locally abundant e.g. in a particular episode following heavy rains in the UK in 2009 (Kibby 2009a,b) that reported 32 occurrences (NBN 2018).

Europe: In Sweden, there are over 130 reports (GBIF 2024). In the UK, it seems widespread, occasionally reported as locally abundant and improving, although this is probably the result of increasing recording efforts in semi-natural grasslands. Elsewhere in Europe, it seems widespread (it is reported from >10 countries), but seemingly rarer (1-10 occurrences; GBIF 2024).

In North America it is rarely reported (MyCoPortal 2024). There are seven reports from the USA: two in 1946 (Oregon), three in 1947 (Oregon), one in 1971 (Hawaii; questionable), one in 1972 (Idaho; not mapped). There is also one report from Canada in 2009 (British Colombia).

Population Trend: Unknown

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Habitat and Ecology

Squamanita paradoxa is an obligate mycotrophic species that parasites a closely related taxon, Cystoderma amianthinum (molecular confirmation; Matheny and Griffith 2010). It belongs to the only agaric genus where all species (ca. 10) are parasitic on other Agaricales. Several Squamanita species appear to fruit over a wide area for two or three years and then disappear from sight for decades. For example, S. paradoxa hasn’t fruited for more than two years at any British site. More recently, one site (ECN Wyddfa, Wales) was specifically surveyed for S. paradoxa over 10 seasons: S. paradoxa was found in four different years, whereas the host C. amianthinum was observed in six of the years (Griffith et al. 2019). In Europe it occurs mostly in grasslands while in North America (Pacific Northwest) mainly in temperate old-growth forests dominated by Douglas Fir and Western Hemlock, with a thick moss understory.

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Threats

As its host, Cystoderma amianthinum is common and widespread, Squamanita paradoxa is not considered affected by any significant threat.

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Conservation Actions

No conservation actions are needed, although further research into the species' population size and distribution, as well as its life history may be useful.

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Use and Trade

There is no use and trade known.

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Source and Citation

Gonçalves, S.C. 2025. Squamanita paradoxa. The IUCN Red List of Threatened Species 2025: e.T125435415A125435690. Accessed on 22 November 2025.

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• Country occurrence