Long known by a misapplied name in the Pacific Northwest, Boletus pulverulentus, this bolete was described as Boletus rainisii (Bessette, Roody, Bessette, 2000) and transferred into Xerocomellus (Frank, 2014). The epithet rainisiae is correct (rainisii is an orthographic variant).
Xerocomellus species are notoriously difficult to identify, and there has been much confusion regarding variation within and among the species. Furthermore, original species concepts and uncertainty about which names to use have added to the confusion. Xerocomellus (Boletaceae) in western North America (Frank, et al. 2020) has redefined western Xerocomellus, and made species determinations easier.
A medium-sized bolete with an olive-brown to yellowish brown cap, with a velvety surface that becomes areolate-cracked in age, yellowish stipe with red tones near the base, and often extensive, dark greenish-blue to bluish-black staining on the lower stipe.
Some of the western North American records of Boletus pulverulentus likely refer to Xerocomellus rainisiae, although some of these records likely involve the similar X. mendocinensis.
The four reported California records, (as Boletus pulverulentus) are likely other Xerocomellus species. There are around 25 locations reported from the Pacific Northwest, but only about 15 are confirmed to be X. rainisiae.
We need to assess based on current records; mostly from old growth forests, but maybe not restricted to this habitat.
Older records need extra scrutiny, because of taxonomic identification issues.
Pacific Northwest of North America, from coastal southern British Columbia, Canada, south through the Olympic Mountains, and east into Cascade Range through Washington, south to at least central Oregon. Exact range poorly known at this time, due to misidentifications of older records.
Little is known of population trends for this species. Misidentification and misapplied names have led to confusion and poor historic records. Many of the recent collection sites are in artificial openings (campgrounds, road and trail edges, etc.) in mature or old growth forests; no records are recorded from younger or 2nd growth forests. More habitat information is needed, and targeted surveys done before trends can be fully assessed.
Population Trend: Uncertain
Scattered to gregarious, rarely solitary, fruiting from duff and soil. Ectomycorrhizal with a host of different conifers, seemingly with a preference for old growth forest. Fruiting in fall and early winter. Many of the recent collection sites are in artificial openings (campgrounds, road and trail edges, etc.) in mature or old growth forests; no recent records (with data available) are recorded from younger or 2nd growth forests.
The current limited extent, and ongoing degradation and loss of old growth forests is likely a primarily threat to populations of this species.
This is a ectomycorrhizal fungus species dependent on living host trees for viability. The major threat to this species and its co-occurring co-generic brethren is habitat destruction, via the logging of old-growth forests to which it appears confined too. The extent of old growth forest in the Pacific Northwest of North America has declined 90% in the last century (Society of American Foresters 1984, Haynes 1986).
Fire is big threat to this species’ populations. A stand replacing fire could severely degrade and/or diminish its current range.
This species should be added to the United States Forest Service Northwest Forest Plan Survey and Manage list of rare/old growth forests dependent fungi. Protect mature and old growth forests in the Pacific Northwest.
Targeted surveys for this species.
More precise habitat information; is this species restricted to old growth forests?
This species, like all western Xerocomellus species, is occasionally collected for food
Bessette, A.E., Roody, W.C. and Bessette, A.R. 2000. North American Boletes A Color Guide to the Fleshy Pored Mushrooms. Syracuse University Press, Syracuse
Frank, J.L. (2014) Index Fungorum 179: 1.
Frank J.L., Siegel, N., Schwarz, C.F., Araki, B. and Vellinga, E.C. 2020. Xerocomellus (Boletaceae) in western North America. Fungal Systematics and
Evolution 6: 265–288
MyCoPortal. 2021. http://mycoportal.org/portal/index.php. Accessed on February 04.
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.