Originally assessed as C2(a)(i) D1, but C2ai with < 1000 individuals would mean EN.
I suggest that we assess it on D only. Else, are you confident with < 1000 mature individuals? I and Greg use as a common proxy to state that 1 genotype/mycelium would correspond to 10 ramets (mature individuals) if not known better. It may be appropriate to use another conversion to mature individuals here (?)
Leucoagaricus hesperius is a robust, medium-sized saprotropic fungus restricted to Monterey cypress (Cupressus macrocarpa) groves in coastal central California, U.S.A., which are characterized by a thick undisturbed litter layer, an open character and the absence of a herbaceous understory. This habitat this species is known from is becoming increasingly rare. It is known from only two such sites. The number of suitable sites is very small, as disturbance of the litter layer, the dying of the overstory trees, and the presence of invasive grasses and herbs have made other locations unsuitable. Though the species is known only from two subpopulations, and has been much looked after, it might be more widespread; it is not easy to identify in the field. The species is estimated to be presented by fewer than 1000 mature individuals in total and in each subpopulation. It is assessed as Vulnerable based on very small population.
Endemic to California, USA. Known from two localities in coastal central California, one in San Mateo County, and one in San Francisco County.
There are only two subpopulations known for the species, one where the species was only found in 1990; in the other locality it has been found several times. It is not known from other locations. Though the species is known only from these subpopulations and has been much looked after, it might be more widespread as it is not easy to identify in the field. The species is estimated to be presented by fewer than 1000 mature individuals in total and in each subpopulation.
Population Trend: Deteriorating
Leucoagaricus hesperius is a rather robust, medium-sized species with a pinkish-reddish brown velvety cap and gills that turn red with age. The fruitbodies become green with ammonia. It is saprotrophic in Monterey cypress (Cupressus macrocarpa) groves, that are open, without a herbaceous understory and with an undisturbed thick litter layer. The spores are wind-dispersed.
In general, the major threats to this habitat are: disturbance of the litter layer, invasion of non-native weeds and grasses such as Vinca major, Ehrharta erecta and Hedera helix, and conversion to oak woodland. Monterey cypress is an endangered species native to California, which has been planted widely as windbreak in coastal areas. The grove in San Mateo County is over 100 years old, and exceptional because of its east-facing slope. It is not open to the public, but disturbance is an issue. The plantation in San Francisco County is very disturbed, and the species has only been collected there once. Disturbance and weed invasions are the main threats.
Raising awareness about the mycological value of Monterey cypress groves with an undisturbed well-developed litter layer. Removal of invasive weeds in suitable habitats, and monitoring of existing sites.
More surveys targeting Monterey cypress groves is needed to fully understand this habitat and its fungal inhabitants.
Vellinga, E.C., 2010. Lepiotaceous fungi in California, U.S.A. Leucoagaricus sect. Piloselli. Mycotaxon 112: 393–444.
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