Tuber castellanoi is a rare member of the T. gibbosum complex, currently known from seven locations in western USA.
Identifying members of the T. gibbosum complex requires careful microscopic examination, and even then, distinguishing the various species can be difficult, and a genetic sequence may be required.

Because of these difficulties, and limited sampling in California, I recommend listing this species as Data Deficient (DD)

Described from a collection made in Sierra National Forest, California, USA (Bonito et al. 2010).

Identifying members of the “Tuber gibbosum complex” (of which T. castellanoi resides) requires careful microscopic examination, and even then, distinguishing the various species can be difficult, and a genetic sequence may be required.

Tuber castellanoi is a rare member of the T. gibbosum complex, currently known from seven locations in western USA.
Identifying members of the T. gibbosum complex requires careful microscopic examination, and even then, distinguishing the various species can be difficult, and a genetic sequence may be required.

Because of these difficulties, and limited sampling in California, I recommend listing this species as Data Deficient (DD)

Widespread but with a highly disjunct distribution: known from the southern Sierra Nevada Mountains, the Klamath Range, and lower elevation and coastal forests in California, Oregon, and Washington (Siegel et al. 2019).

Widespread but with a highly disjunct distribution: Currently known from 9 collections spanning 7 locations; this may be due a limited scientific sampling (and sequencing) of Tuber species from this area. Being recently described, there is not enough data to assess trends.

Hypogeous, scattered under duff and in soil; mostly in drier woodlands with Douglas-fir, (Pseudotsuga menziesii), pines (Pinus spp), White Fir (Abies concolor), and oak (Quercus spp.). The type location (southern Sierra Nevada, Claifornia) had Abies concolor, Pinus lambertiana, Pinus ponderosa, and Calocedrus decurrens. Some sites were Pseudotsuga menziesii monoculture. Fruiting in winter and spring. This species is dependent on mycophagy (primarily eaten by small mammals) for spore dispersal.   

Members of the Tuber gibbosum complex are highly sought-after, commercially traded species. Harvest by indiscriminately raking the duff and topsoil to expose the truffles, (a common practice) is certainly detrimental to the habitat, and long-term viability of this species (and the other species with which it co-exists; including not only other fungi, but also duff and soil-dwelling animals and herbaceous plants).

No specific conservation actions are needed with regards to this species.

More sampling and sequencing of Tuber species in western North America.

Members of the Tuber gibbosum complex (of which T. castellanoi resides) are highly sought after edible species.

Bonito, G., Trappe, J.M., Rawlinson, P., Vilgalys, R. 2010. Improved resolution of major clades within Tuber and taxonomy of species within the Tuber gibbosum complex. Mycologia 102: 1042–1057.

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.