R-L categories correct, but text here does not match final assessment. Updated version will be published in IUCN´s Red List June or Nov 2019.
Hygrocybe aurantiosplendens is a typical representant of the rich mycoflora of old, unimproved grasslands, a habitat type that is decreasing fast in entire Europe. The species is very striking by size and bright orange basidiocarps and usually well distinguishable from related species. It is almost only known from Europe, with very few localities in Asia. In Europe H. aurantiosplendens is widespread, but rare to very rare everywhere (Boertmann, 2010) and decreasing, reflected by its classification in many national and regional Red Lists.
Based on the continuing and projected decline of the global populations of approximately 40% in three generations (50 years) and its restricted and fragmented area of occupancy, Hygrocybe aurantiosplendens is preliminary assessed as Vulnerable based on the criteria A4c and B2ab.
Most parts of Europe; two isolated localities in Russian Far East.
Hygrocybe aurantiosplendens is widespread in Europe, but rare to very rare everywhere (Boertmann, 2010) and decreasing. Besides it is known from two populations in one area (Nature reserve Kedrovaya Pad in Primorsky Kray region) in the Russian Far East (Asia). It occurs from sea level up to the alpine zone (2500 m in the Alps). The area of occurrence is very large, but the area of occupancy is estimated at less than 1000 km2 and this area is strongly fragmented. The total number of individuals is unknown. In view of the strong decrease of unimproved grasslands in the last 50 years (estimated three generations of this fungus), the number of localities must have decreased by at least 30%, possibly over 50%. The decline is reflected in the position of H. aurantiosplendens on many national Red Lists, e.g. Endangered in Denmark, Finland, France, Poland; Vulnerable in Austria and Germany; Near threatened in the Netherlands, Norway, Sweden. The decrease is still continuing.
Population Trend: Decreasing
Hygrocybe aurantiosplendens is a characteristic species of old, unimproved, low productive grasslands on loamy, weakly acid to basic, often calcareous soils. It occasionally grows also in scrub and deciduous forests on moist to dry, base-rich soils. Like other waxcaps the species lives probably in biotrophic association with herbaceous plants, but details are unknown yet.
Threats are grassland improvement (fertilizer application and soil disturbance) for agro-industry farming, abandoning of low productive grasslands, and forest plantations on poor grassland sites. Moreover the species is vulnerable for acidification and nitrogen deposition (Arnolds, 2015).
The most important action will be conservation of sites with rich populations of Hygrocybe aurantiosplendens as nature reserves; continuation of traditional management: mowing and removal of sward or/and grazing in low densities without fertilizer application. The species is a representant of a rich mycoflora with many more rare and threatened species; therefore its protection will be benificial to many more threatened fungi (Boertmann, 2010; Arnolds, 2015).
More detailed research on habitat requirements and habitat exploitation of H. aurantiosplendens would be useful.
Arnolds, E. in C. Bas et al. 1990. Flora agaricina neerlandica 2.
Arnolds, E. 2015. Wasplatengraslanden in Nederland. Deel 1. Ecologische en vegetatiekundige aspecten. Stratiotes 47: 45-75.
Boertmann, D. 2010. The genus Hygrocybe.
Candusso, M. 1997. Hygrophorus sl. Fungi Europaei 6.
Krieglsteiner, G.J. 2001. Die Grosspilze Baden-Württembergs 3.