Assessment Notes

Justification

Lepiota scaberula is a very rare species, only known from two localities in California, U.S.A. It is a relatively small pale brownish-tan species with uplifted scales on the cap and a reddening stem. It is easy to recognize from other Lepiota species because of its special structure of the cap surface in which uplifted scales give rise to loose cells. The two locations are around 4–5 miles apart, one is a Monterey Cypress grove which is more than a century old and the other a Coast Redwood forest. Despite intensive inventories in suitable habitat in close proximity to these two populations, it has not been recorded from other locations. The Monterey Cypress grove is under constant threat to be converted in to an oak woodland, as the grove is considered non-native in this particular location - if this were to occur, Lepiota scaberula would rapidly become Critically Endangered. It has a very small and restricted population, occupying a small area of less than 20 square km, and one locality and its habitat is under constant threat of deterioration. The species has been looked for in other similar habitats in the last 10 years but has not been observed. The total population is estimated to occupy not more than 5 locations and not to exceed 1000 individuals. It is assessed as Vulnerable based on a very small and restricted population.

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Taxonomic notes

Lepiota scaberula belongs to a small clade of species with a special type of pileus covering, in which uplifted cells give rise to globose cells that get detached. The other two known species in this clade occur in the Mediterranean area (the L. cystophoroides / Cystolepiota cystophora complex in southern Europe, and north Africa; L. albogranulosa in Pakistan) (Qasim et al., 2015). Lepiota scaberula is, as far as known, the only North American representative of this clade, and hence, phylogenetically unique in this continent.

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Geographic range

Endemic to California, USA. Known from only 2 locations, around 5 miles apart in San Mateo County.

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Population and Trends

Very small and restricted population, occupying a small area of less than 20 square km, and one locality and its habitat is under constant threat of deterioration. Based on fruitbody inventories and surveys, Lepiota scaberula is known from only two localities, both in San Mateo County, California, USA, viz. the San Francisco Watershed area near Crystal Springs reservoir, and Wunderlich County Park. Despite frequent visits to similar habitats (Coast redwood forests and Monterey cypress groves in San Mateo and Santa Cruz counties), L. scaberula has only been found in these two localities. The species has been looked for in other similar habitats in the last 10 years but has not been observed. Due to its rarity, it is difficult to state anything about trends of L. scaberula.

Population Trend: stable

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Habitat and Ecology

Two populations are known, one in a >100 year old Monterey Cypress (Cupressus macrocarpa) grove on an east facing slope, and one in a Coast Redwood (Sequoia sempervirens) forest (Vellinga 2001). The Monterey Cypress grove is characterized by an undisturbed duff layer, and it harbours a number of very rare Lepiota and Leucoagaricus species. Two other species that are growing here, Lepiota rhodophylla and L. luteophylla, have also been proposed to soon be assessed for the IUCN Red List. The nutritional mode of Lepiota scaberula is saprotrophic. The spores are wind-dispersed.

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Threats

The Monterey Cypress location is under various threats.  Access to the area is restricted, but its mycological richness attracts trespassers. The undisturbed duff layer and the lack of undergrowth are the main characteristics that allow for the mycological richness. A similar grove in the same restricted area is overgrown by Vinca major, basically eliminating all fungal growth. Trampling by humans and deer would change the character and the suitability for Lepiota species. The other fact that sets this particular grove apart is its location on an east facing slope. The Monterey Cypress grove was planted in the early 1900s and is considered non-native in the present location. Monterey Cypress is a native tree species of California, but considered native in only a very few locations on the coast. Plantings have also mostly taken place on west-facing slopes right on the coast. Management proposals to convert the present Monterey Cypress grove into native oak forests have been thwarted for the time being, but could be rescinded. The Coast Redwood location is in a park and not under threat.

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Conservation Actions

Awareness of the rarity of the taxon has to be raised, and the two known populations have to be monitored. Monterey Cypress groves in general have to be put off-limits to disturbance, so that the duff layer can develop. The Monterey Cypress grove is home to a number of very rare and endangered Lepiota and Leucoagaricus species, and should be maintained and not converted into Oak and Douglas Fir woodlands.

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Use and Trade

Not applicable.

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Source and Citation

Vellinga, E.C. 2019. Lepiota scaberula. The IUCN Red List of Threatened Species 2019: e.T125433519A125435460. https://dx.doi.org/10.2305/IUCN.UK.2019-1.RLTS.T125433519A125435460.en .Accessed on 1 February 2024

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• Country occurrence