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. Most western records of Boletus pulverulentus likely refer to Xerocomellus rainisiae, although some of these records might involve the similar X. mendocinensis. Reported from four sites in California, (as Boletus pulverulentus), with twenty-five Pacific Northwest records.
Occurring on the north coast of California, USA, inland to Mount Shasta, with an unconfirmed report from the northern Sierra Nevada; from the coast to the Cascades in Oregon and Washington and on Vancouver Island in British Columbia, Canada
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 (campground
(All threats are hypothetical, as little is known about this species). The current limited extent, and ongoing degradation and loss of old growth forests is likely a primarily threat to populations of this species.
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
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.