Cortinarius olsoniae

Also known as Cortinarius ‘winter blues’ in Mushrooms of the Redwood Coast

Cortinarius olsoniae N. Siegel, S.D. Adams & Bojantchev, sp. nov.

Holotype WTU F-075672, NS 01192013-1


Pileus 20–80 mm broad, conical when young, becoming broadly conical to convex, often with a low, broad umbo, margin inrolled, often squared off when young, becoming downcurved to plane, then wavy and occasionally uplifted in age. Surface smooth, shiny, moist to slightly viscid when wet; dull, appressed-fibrillose when dry, strongly hygrophanous. Color extremely variable; when wet deep purple, becoming silvery purple and finally purplish tan to purple-brown, in dry conditions: silvery blue to bluish purple with appressed silvery fibrils, becoming bluish tan to purplish tan and finally grayish tan. Lamellae adnate to slightly adnexed, close to moderately crowded, broad. Beige at first, becoming cinnamon tan and then darker ocher-brown as spores mature. Stipe 40–140 x 5–15 mm, equal or slightly enlarged downward, then with a tapered, “rooting” base; surface dry to slightly moist, covered with silky fibrils when young, smooth in age; whitish with a band of violet or bluish color below partial veil, developing dingy tan stains in age. Cortina thin, sparse, binding to cap margin and leaving a silky annular zone of whitish fibrils on stipe. Context thin, brittle, purplish to purple-brown in cap; stipe fibrous, solid to stuffed, tan. Odor and taste indistinct. KOH no reaction.

Microscopy: Spore deposit rusty brown. Basidiospores (120/4 collections) (8·5–) 8·5–11 (–12) x (4·5–) 5–6·5 (–7) μm, avg. 9·86 x 5·74 μm, Qr 1·45–2·06, Qa 1·72, weakly roughened to nearly smooth. Basidia 24–36 (–41) x (6–) 7–10 μm, cylindrical-clavate, hyaline, 4-spored. Pileipellis composed of periclinal hyphae 3·5-8 μm. Septa with clamps.

Ecology and Distribution

Solitary or scattered on ground in coastal Picea sitchensis forests. Fruiting in winter, after the primary fall season.


Photographs #1 and #3 are shared by Noah Siegel and published as Cortinarius ‘winter blues’ in Mushrooms of the Redwood Coast (2016). The remaining photographs are courtesy of Joann Olson and iNaturalist.


This species was named for Joann Olson, a Cortinarius enthusiast from Humboldt County, California, who first collected this species. It was given the provisional name of Cortinarius ‘winter blues’ in Mushrooms of the Redwood Coast (2016)

Cortinarius olsoniae is in Subgenus Telamonia Section Bicolores. Genetically the species is closest to C. subcagei, but has only 97% similarity to this species with 15 base pair differences. This beautiful winter-fruiting Cortinarius can look like two different species depending on the dryness of the fruiting conditions—markedly purple when wet, silvery blue when dry. In addition to the variable cap color, this species can be recognized by the pallid gills, somewhat rooting stipe with whitish or purplish blushes, and preference for fruiting late in the season. In Humboldt County, it produces basidiomata one-to-two months after most other Cortinarius. Appears quite rare: currently only known from a restricted range on the Pacific Coast, with Picea sitchenensis.

Specimens Examined

USA: California, Humboldt Co., Redwood National Park, Davison Road, 1 km east of Gold Bluff Beach in Picea sitchensis forest; 19 Jan. 2013, N. Siegel, NS 01192013-1 (Holotype), GenBank OP748989. 1 Feb. 2016, N. Siegel, NS 02012016-1, (WTU F-075675), GenBank OP748990. 20 Jan. 2016, J. Olson JO-01, (WTU F-075673), GenBank OP748987. 9 Jan. 2018, J. Olson, JO-02, (WTU F-075674), GenBank OP748988.


Kare Liimatainen et al., “Mission Impossible Completed: Unlocking the Nomenclature of the Largest and Most Complicated Subgenus of Cortinarius, Telamonia,” Fungal Diversity, September 8, 2020,

Siegel, Noah and C. Schwarz (2016), Mushrooms of the Redwood Coast—a comprehensive guide to the fungi of coastal
northern California.Ten Speed Press, Crown Publishing Group, Berkeley CA

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