Assessment Notes

Justification

Hygrophorus caeruleus is a medium-sized mushroom, typically buried under duff, fruiting in spring and early summer. It can be recognized by the silvery-blue, bluish gray to bluish green color, short, stocky stature and often strong, rancid-farinaceous odour. It is currently reported from approximately 30 sites over a wide area, and due to its often cryptic fruiting habit (under duff) is likely to be highly under-reported. Data to assess population trends are lacking, but there are a number of recent reports. Considering these factors, it is assessed as Least Concern (LC).

---

Taxonomic notes

This species was described based on a collection made near McCall, Idaho, USA (Miller 1984). Recent genetic analysis has shown close affinity with Clitocybe sensu lato, and it likely will get transferred to Clitocybe or a segregate genus in the near future.

---

Geographic range

It occurs from the southern Sierra Nevada mountains in California north through the Cascade Range into Washington, and east into the northern Rocky Mountains. Typically it is found in drier forest habitats.

---

Population and Trends

The population is widespread in the western mountains of USA; currently known from around 30 sites. The often cryptic growth (buried under duff) makes this species hard to find, but because of the blue colour and bad smell it rarely goes unreported if found. Not enough data exist to assess trends, but based on what is known about the habitat preferences it is likely to be stable.

Population Trend: stable

---

Habitat and Ecology

This species is solitary, scattered, or in small clusters; typically buried under duff and litter. In California it seems to prefer White Fir (Abies concolor) forest but can be found in duff under most conifers. Unless it is growing in an area with hard packed soil, and limited duff, it is rarely exposed; but it will push up the duff, forming “shrumps”. Fruiting occurs in spring, soon after snowmelt, continuing into summer. Nutritional mode is not known (Siegel et al. 2019). The often-buried fruiting bodies and strong odour are suggestive of a species that is, at least somewhat dependent on mycophagy (primarily eaten by small mammals) for spore dispersal. Wind dispersal is probably still important, but to a lesser extent (Siegel 2017).

---

Threats

Prolonged droughts and decades of fire suppression have drastically altered the high Sierra forests, leading to thicker, denser, Abies-dominated forest. As a result hotter, stand-replacing fires (rather than patchwork and understory burns) are commonplace, altering appropriate habitat drastically, burning much of the available large woody debris apparently necessary for this species’ habitat. Climate change leading to a reduction in snowpack in the western North American mountains has limited suitable habitat for this species, which only appears to occur after wet winters.

---

Conservation Actions

This species was included on the US Forest Service Northwest Forest Plan species of special concern (Castellano et al. 1999). Recent genetic analysis has shown close affinity with Clitocybe sensu lato, but additional work on generic placement is needed.

---

Use and Trade

No use/trade is known.

---

Source and Citation

Siegel, N. 2021. Hygrophorus caeruleus. The IUCN Red List of Threatened Species 2021: e.T195923922A195926098. https://dx.doi.org/10.2305/IUCN.UK.2021-2.RLTS.T195923922A195926098.en .Accessed on 5 October 2024

---

• Country occurrence