Assessment Notes

Justification

Agaricus pattersoniae is restricted to mature Cupressus macrocarpa stands with an undisturbed duff layer in central coastal California. Its habitat is threatened by developments, decline of Cupressus due to infection with Seiridium cardinale and increasing drought. Conservation of mature C. macrocarpa stands and younger stands that will provide the habitat in the future will effect a number of species that are restricted to this habitat, such as Lepiota and Leucoagaricus species plus other Agaricus taxa.

Agaricus pattersoniae is assessed as Vulnerable (VU) under criterion C2a(i) as the number of known localities is small (less than 50) and the number of mature individuals numbers about 1,000 with each subpopulation having fewer than 500 mature individuals. It also almost fulfill the criteria for A3c for VU as the number of sites is declining and projected to decline by about around 25% in the next 20 years.

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Taxonomic notes

Originally described as Agaricus pattersonae.

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Geographic range

Agaricus pattersoniae is probably endemic to California as it only is known from the central coastal region in California (USA): Sonoma County southwards into San Luis Obispo County. A few reports are from the eastern part of the USA but these have to be confirmed.

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Population and Trends

Agaricus pattersoniae is known from less than 50 sites based on collections (Mycoportal.org) and recent observations (2009-2015; Mushroomobserver.org) in California (USA). The species and its habitat are currently stable, but is prone to future decline of cypress groves. The fungus grows in the original Cupressus macrocarpa stands, and secondary occurrence in planted stands. C. macrocarpa is native to California where it occurs in two main subpopulations, but is widely planted as windbreaks in coastal areas around the world.

Population Trend: stable

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Habitat and Ecology

Agaricus pattersoniae is saprotrophic in duff of mature (over 40 years old) Cupressus macrocarpa stands and groves with an undisturbed duff layer, fruiting from (November) December through March, after heavy winter storms. The species does not occur under solitary trees or stands with a well-developed herb and grass layer.

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Threats

Cupressus macrocarpa is endemic to California, and occurs in two main natural subpopulations; planted groves exist, but are considered non-native and are threatened with replacement by native tree species. C. macrocarpa is prone to infection by Seiridium cardinale which damages and kills older and more exposed trees. Habitat destruction is the main threat; for instance the cypresses at the type locality have been removed. Due to the absence of late winter rains in the winters of 2012-2015 the species has not been fruiting in its usual localities. C. macrocarpa is currently assessed as Vulnerable on the IUCN Red List because of its restricted range and susceptibility to increased risk of fire due to future climate change.

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Conservation Actions

Most of the main stands of  Cupressus macrocarpa are protected, however, the habitat needs to be properly managed, especially to reduce the risk of fires in the future.

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Use and Trade

This is edible like most Agaricus species

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Source and Citation

Vellinga, E. 2015. Agaricus pattersoniae. The IUCN Red List of Threatened Species 2015: e.T75093504A97167420. https://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T75093504A75094030.en .Accessed on 9 February 2024

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• Country occurrence