Cortinarius fulminoides is associated mainly with Abies spp (Abies alba, A. nordmanniana), sometimes in mixed Abies-Pinus forests, very rarely seen also in pure Picea abies forests. Its major habitat is montane, calcareous Abies- or Abies-Picea-Fagus forests of C and S Europe, a forest type with many habitat-specific taxa of Cortinarius, subgenus Phlegmacium. 
The Phlegmacium-rich, calcareous Abies or mixed Abies-Picea-Fagus forests often occupies small and fragmented areas, and the habitat is vulnerable of habitat loss due to urbanization, lime quarries, shift in tree species (uniform Picea plantations or Picea expansion due to selective deer overgrazing), climate warming with severe droughts, etc, and to decreased ecological conditions due to modern forestry (with clear-cuts). 
Global red-list assessment: The species is known from approx.. 25 localities in Europe/globally. The total population is estimated to approx. 250 localities, which is equivalent to approx. 5,000 individuals according to IUCN standards. According to the C criterion (C2 a(i)), the species becomes red-listed as VU, based on a continuous decline, population size <10 000 individuals and very small/isolated subpopulations.

Cortinarius fulminoides is a little known, phlegmacioid species with vivid yellow-brown to leon-brown or apricot brown pileus colours, whitish stipe, and small, distinctly ornamented spores, measuring 7.5-9 x 5-5.5(-6) µm. The species may resemble C. glaucopus, but differs on the complete lack of bluish tinges on young lamellae and stipe. The species belongs to the section Aureocistophili, which is rather close to sect Glaucopodes (Soop et al. 2019). Within Aureocistophili, C. fulminoides resembles C. subrugulosus, which might occur in the same habitats, but the latter has more silvery white veil remnants upon pileus (Soop et al. 2019). Cortinarius kytoevuori, known only from Picea-Pinus forests from Finland, is apparently also very similar.

Cortinarius fulminoides is a almost strictly European species being habitat-specific for declining forest types; calcareous Abies alba and Abies nordmanniana forests.

According to present data, Cortinarius fulminoides is mainly distributed in the montane regions with (mixed) Abies alba forests of the Jura and Prealps. It is known also from the eastern Pyrenées, and from the montane Abies nordmanniana forests of W Caucasus. The species probably has a wider distribution within the natural Abies alba range of the Carpathians, the Italian Apennines and the Balkan-Greech mountains (but the calcareous fir forests are little investigated in most of these regions). Outside the natural Abies forest range, the species is recorded once under Picea abies in E Sweden. There are also a few finds from N America (California, Quebec), with slightly deviating ITS-DNA sequences.
The latter finds deviate from the normal pattern of the element of habitat-specific taxa of calcareous Abies forests; almost all species are lacking outside Europe.

Cortinarius fulminoides is known from approx. 25 sites/localities globally; most records are from the Jura-Prealps-Black Forest region; E France-SW Germany-Switzerland-Austria-N Italy, furthermore a few from NE Spain, one from Russuian Caucasus, and an ITS-sequence-verified northern outpost in E Sweden and finally a few verified from California and Quebec. The total population is estimated to approx. 250 sites/localities, which is equivalent to approx. 5,000 individuals, according to IUCN standards.
The decline of the calcareous Abies forests (or mixed Abies-Picea forests) in the evaluation period (last 75 years) is estimated to be in the magnitude of 15-20%. The species becomes red-listed as VU, according to the C criterion (C2 a(i)), based on a continuous decline, population size

<10 000 individuals and very small/isolated subpopulations (According to the A-criterion (A2c + 3c + 4c), the species becomes red-listed as NT (species/habitat decline >

15%).

Cortinarius fulminoides is associated mainly with montane calcareous, herb-rich-mossy Abies or Abies-Picea-Fagus forests, where it forms mycorrhiza with Abies alba, in Caucasus with Abies nordmanniana. The species apparently rarely also associate with Picea abies in areas with mixed Abies-Picea forests. North of the natural Abies alba forest range, the species is once recorded in pure Picea abies forest. The species regularly occur together with other species of the calcareous Abies forest element, such as C. atrovirens, C. haasii and C. subgracilis.

Cortinarius fulminoides and its habitats (calcareous Abies(-Picea) forests) have been declining e.g. due to areal loss (urbanization, expansion of limestone quarries, shift from Abies stands to Picea by planting, and as selective overgrazing and bark stripping by deers, climate warming with severe droughts) as well as decreased habitat quality/ecological conditions due to modern forestry with clear-cuttings (Bledy et al. 2024). Forest statistics from Austria indicates that forestry activity has been doubled the last 40 years, and according to a habitat-redlist in Austria, the Abies-Picea forests are endangered in many regions of Austria. Severe decline and die-back of Abies alba forests was reported already 40 years ago due mainly to SO2 air pollution. In recent years, the decline is apparently due to a complex mix of factors (Bledy et al. 2024). Decline of Abies alba forests in recent years is reported from several C & S European countries, such as Austria, Czech Republic, Italy, Slovenia, N Spain, etc.

To prevent decline and further fragmentation of calcareous Abies (-Picea) forests with good habitat quality, it is important to set aside reserves on calcareous hotspots, housing many rare/redlisted, habitat-specific species such as C. atrovirens, C. camptoros, C. citrinoolivaceus, C. fulminoides and C. haasii. It is furthermore important to establish also sites with a less strict conservation regime, such as woodland key biotopes, where some non-destructive human activities are accepted (such as non-intensive forestry, with closed cutting).

More mapping/surveying and monitoring of C. fulminoides is needed. More data on occurrences in the little studied calcareous Abies alba forests of the Carpathians and the montane regions of Balkan-Greech is especially needed. Finally, more documentation on the degree and causes of decline of the habitats themselves is needed.