Assessment Notes

Justification

Lepiota rhodophylla is known only from the type locality, a small area  at the San Francisco Watershed, California, USA. The type habitat is one of the few remaining large-scale groves of Monterey Cypress (Cupressus macrocarpa) that have a well-developed duff layer. 

Planted Monterey Cypress are severely impacted by infection of the fungal disease Cypress Canker (Seridium cardinale). This tree (which dominates and defines that habitat at the type location) is listed as Vulnerable due to its tiny native range (two relict populations in Monterey County, California).

The pink lamellae are diagnostic within the genus, and should draw attention and special notice even when encountered by casual mushroom enthusiasts. A thorough search of mushroom observations generated by citizen-scientists in California did not reveal any candidate observations. It is possible that this species is being overlooked due to confusion with immature Agaricus species. However, this is relatively unlikely given increasing sophistication of taxonomic observers in this area, and that many taxa that are more difficult to identify or less-conspicuous are regularly recorded by such communities of enthusiasts.Based on the apparently small population size, this species is assessed as Critically Endangered.

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Taxonomic notes

This species is readily recognizable (as long as the genus is correctly ascertained) by the pink lamellae and stout stature of the fruitbodies (Siegel and Schwarz 2016).

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Geographic range

This species was described from and is currently known only from a small area in the San Francisco Watershed, San Mateo County, California, USA (Vellinga 2006).

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Population and Trends

The only site known probably represents a single mycelium likely representing one genet, where it has been recorded five times during two seasons (2000, 2002-2003). Despite its characteristic appearance and intensive surveys specifically aimed at inventorying Lepiota and Leucoagaricus taxa associated with Monterey Cypress during 2002-2003, this species was not encountered elsewhere (E. Vellinga pers. comm.). Broader surveys of Monterey Cypress in central California from 2010-2016 also did not encounter this species (N. Siegel and C. Schwarz pers. comm.).

Given the absence of comparable habitats, old, extensive, East-facing, inland Monterey Cypress groves, very few similar potential sites are estimated to exist. The total number of sites is estimated not to exceed five and the total population of mature individuals is less than 50.

Population Trend: unknown

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Habitat and Ecology

Lepiota rhodophylla is a saptrotrophic fungus growing on duff of Monterey Cypress, Cupressus macrocarpa, and like many of California’s Lepiota, Leucoagaricus and Agaricus, it is primarily associated with Monterey Cypress. These fungi appear to have very strong habitat preferences and many of them are rarely or never encountered in other habitats.

Fruiting events for Lepiota rhodophylla are likely annual, but may be somewhat opportunistic as for many duff-decaying species found under Monterey Cypress, with potential to occur at any point in the wet season.

Stands of Monterey Cypress in coastal California are rich in lepiotaceous species, white-spored members of the family Agaricaceae (Vellinga 2006). A high number of these species may grow together in a small area, such as a single Monterey Cypress stand in the San Francisco Watershed, where 25 species were encountered in the 2002-2003 mushroom season (Vellinga 2004). Although Monterey Cypress is very widely planted, the trimmed hedges, windrows, and singletons that are most commonly encountered lack accumulations of duff, and do not form closed canopies, and thus do not appear to be suitable habitat for many of the rarer fungi that associate with larger groves of Monterey Cypress. Of the few older stands of this tree that do exist (most of which are planted), only a few have a well-developed duff layer. Even among these sites, there appears to be significant heterogeneity in the occurrence of cypress-associated fungi for these refugia, perhaps limited by constraints on dispersal.

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Threats

Very few large-scale groves of Monterey Cypress-dominated habitat exist. This tree (which dominates and defines that habitat at the type location) is listed as Vulnerable due to its tiny native range (two relict populations in Monterey County, California): The native range of the tree is represented by two very small groves with a total estimated area of occupancy (AOO) of 13 sq. km or less.

The naturalized groves of Monterey Cypress are at risk of destruction by fire, drought stress, and other impacts related to climate change.  Plantings of these trees near human settlements are often severely degraded by the removal of lower limbs and duff (making the habitat less suitable for associated litter-inhabiting fungi), as well as by extensive intrusion smothering the duff layer by a number of invasive plants including Hedera helix, Delairea odorata, and Vinca major.

The only known site for Lepiota rhodophylla is unique, in that it is on an east-facing slope, away from the cooler climate of the coast where the other suitable sites are. This makes the habitat more vulnerable to Seiridium cardinale (Cypress Canker). Furthermore, the land management practice at the site is predisposed to removal of this tree. These two factors combined increase the likelihood that the type locality will be degraded. Planted Monterey Cypress are severely impacted by infection of the fungal disease cypress canker (Seiridium cardinale) (Graniti 1998).

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Conservation Actions

The following conservation actions are required:

• Survey existing groves of Monterey Cypress (both in native range as well as in planted groves) to determine whether the known population from the type locality is still extant, and whether other populations exist. 
• Develop interpretive materials for use at state parks, watersheds, state property, and public lands where Monterey Cypress groves exist.
• Work to develop understanding that existing groves which act as refugia for Monterey Cypress mycoflora should be protected.
• Recommend to land managers in more urban areas that groves of Monterey Cypress be managed in such a way that the duff layer remains as intact as possible (avoid removing lower limbs, avoid raking duff, limit foot traffic).
• Remove invasive vines and other plants from existing Monterey Cypress groves, especially Common Ivy (Hedera helix), Cape Ivy (Delairea odorata), and Greater Periwinkle (Vinca major).

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Source and Citation

Schwarz, C. & Vellinga, E.C. 2017. Lepiota rhodophylla. The IUCN Red List of Threatened Species 2017: e.T95384531A95385514. https://dx.doi.org/10.2305/IUCN.UK.2017-3.RLTS.T95384531A95385514.en .Accessed on 3 February 2024

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• Country occurrence