Gastroboletus citrinobrunneus is a rare and poorly known species, recognized by the irregularly convex, bright yellow and brown cap, yellow pores and dark blue staining on all parts. Known from five collections, from three locations in the northern Sierra Nevada and southern Cascade Range of California, USA, in mid- to high-elevation Abies forests. Targeted surveys for this species are needed to document its actual distribution and rarity . While it likely occurs in other sites, the fact that this brightly colored, distinctive species has so infrequently been recorded suggests that it is rare.  Population size is very cautiously estimated to be between 1,000-2,000.  As Sierra Nevada forests have undergone significant changes over the past 40 years due to insect damage, drought, and wildfires, the population of G. citrinobrunneus is estimated to have declined between 30%-50% over its past three generations with declines continuing into the future. Previous to the loss of habitat due to these threats, the population was likely relatively intact.  Due to its small populations size and population decline it is assessed as Endangered.

Described from a single collection made near Mineral, in Tehama County, California, USA (Thiers 1979).

The genus Gastroboletus accommodates a number of species with semisequestrate to sequestrate fruitbodies. These morphological forms have evolved multiple times, within different genera of boletes. Some of these species have been transferred to their ancestral genera, while for others, such as G. citrinobrunneus, the closest relatives are not known yet (Siegel et al. 2019).

Gastroboletus citrinobrunneus is a rare and poorly known species, recognized by the irregularly convex, bright yellow and brown cap, yellow pores and dark blue staining on all parts. Known from five collections, from three locations in the northern Sierra Nevada and southern Cascade Range of California, USA, in mid- to high-elevation Abies forests.  Targeted surveys for this species is needed before to document its

Mid- to high-elevation forests in the Norther Sierra Nevada and Southern Cascade Mountains in California, USA. Known from mid to high-elevation in the northern Sierra Nevada and southern Cascade Range. Currently known from four collections from two voucher-confirmed locations: Tehama Co.,  near Mineral (Type) and Sierra Co near Yuba Pass and third from Plumas Co. National Forest, near Lake Davis. is unconfirmed.

Very rare, only known from three locations, and five collections. More collections, a better understanding of this species, and knowledge of suitable habitat are needed to properly assess population and trends of this species. While it likely occurs in other sites, the fact that this brightly colored, distinctive species has so infrequently been recorded suggests that it is rare.  Population size is very cautiously estimated to be between 1,000-2,000 based on an prediction that the species occurs in 100-200 additional sites, each with up to 10 mature individuals (Dahlberg and Mueller 2011).

Sierra Nevada forests have undergone significant changes over the past 40 years.  Steel et al 2023 report that 30% of the region’s conifer forest extent has been converted into nonforest vegetation during 2011–2020 due to insect damage, drought, and wildfires and the population of G. citrinobrunneus is estimated to have declined between 30%-50% over its past three generations with declines continuing into the future.  Previous to the loss of habitat due to these threats, the population was likely relatively intact.

Occurring in mid- to high-elevation fir (Abies) forests. Fruit bodies are completely buried to partially exposed in duff or soil. Ectomycorrhizal, likely associated with White Fir (Abies concolor) and Red Fir (Abies magnifica), and possibly other members of Pinaceae. Fruiting in summer. This species is likely dependent on mycophagy (primarily eaten by small mammals) for spore dispersal.

Prolonged droughts and decades of fire suppression have drastically altered the high Sierra Nevada forests, leading to thicker, denser, Abies dominated forests. As a result, hotter, stand replacing fires (rather than patchwork and understory burns) are commonplace, altering appropriate habitat drastically, and making it ill-suited for this species.

Protect known sites from management activities, including logging, fuels reduction, or other development and disturbance. Add to USFS sensitive species list.

Modern taxonomic work is needed on this species; how does it differ from Gastroboletus turbinatus var. flammeus?
Historic sites should be revisited and appropriate habitat surveyed for this species.

None known.

Siegel, N., Vellinga, E.C., Schwarz, C., Castellano, M.A. and Ikeda, D. 2019. A Field Guide to the Rare Fungi of California’s National Forests. Bookmobile: Minneapolis, MN. 313 p.

Steel, Zachary L., Gavin M. Jones, Brandon M. Collins, Rebecca Green, Alexander Koltunov, Kathryn L. Purcell, Sarah C. Sawyer, et al. 2023. “ Mega-Disturbances Cause Rapid Decline of Mature Conifer Forest Habitat in California.” Ecological Applications 33(2): e2763. https://doi.org/10.1002/eap.2763

Thiers, H.D. 1975. California Mushrooms – A Field Guide to the Boletes. Hafner Press.

Thiers, H.D. 1979. New and interesting hypogeous and secotioid fungi from California. Beihefte zur Sydowia 8:381–390.

Thiers, H.D. and Trappe, J.M. 1969. Studies in the genus Gastroboletus. Brittonia. 21(3):244-254