Phlegmacium myrtilliphilum is a species of mushroom-forming fungus in the family Cortinariaceae, first described in 2014 as a member of the genus Cortinarius before being reclassified in 2022. It is characterized by its medium-sized fruit bodies with pale yellowish-brown to ochraceous caps, greyish-white gills that turn pale brown with age, and distinctively shaped spores with an elongated apex. This fungus grows in mesic spruce-dominated forests with bilberry (Vaccinium myrtillus) understory, from which its name derives. Currently known only from the middle boreal zone of Finland and Norway, it appears to be relatively rare and produces its fruiting bodies in autumn.
The species was described in 2014 and classified as Cortinarius myrtilliphilus. The type specimen of was collected on 14 September 1997 by I. Kytövuori (no. 97âÂÂ1469) in SuolijärviâÂÂSiikajärvi, at the northâÂÂwest foot of Siikavaara (Rönninvaara) in the municipality of Suomussalmi, Kainuu, Finland. The fungus was found in a gently sloping, partly swampy grassâÂÂherbâÂÂPicea forest with scattered Pinus, Betula, Populus, Alnus incana and various Salix species. The holotype (H6032751) is preserved at the herbarium of Helsinki University (H), and an isotype (duplicate) held at the New York Botanical Garden (NY).
The fungus was placed in the subgenus Phlegmacium of the large mushroom genus Cortinarius. The specific epithet myrtilliphilum (originally myrtilliphilus) alludes to the association with Vaccinium myrtillus plants. In 2022 the species was transferred from Cortinarius and reclassified as Phlegmacium myrtilliphilum based on genomic data.
Phlegmacium myrtilliphilum produces a mediumâÂÂsized fruit body with a cap (pileus) measuring 4.5âÂÂ9 cm broad, initially hemispherical and becoming planoâÂÂconvex, its margin slightly incurved. Young caps are weakly to distinctly viscid from a thin, soonâÂÂdrying veil, showing appressed scales, especially at the centre. Colour varies from pale yellowishâÂÂbrown to darker ochraceous or leather brownâÂÂreminiscent of Cortinarius balteatusâÂÂwith a paler, almost whitish margin and occasional hygrophanous streaks (bands that change hue as the cap loses moisture). The gills (lamellae) are emarginate (notched where they meet the stipe), crowded, greyish white in youth and turning pale brown as spores mature. The stipe is 5.5âÂÂ11 cm long, 1âÂÂ2.5 cm thick near the apex and 1.5âÂÂ3 cm wide at the base, clavate, white at first, then pale brown from the base. A sparse white universal veil may leave remnant patches. The flesh (context) is white, faintly greyish hygrophanous at the stipe apex, and emits a faint, pleasant odour resembling corn. In dried specimens, the pileus is uniformly pale warm yellowishâÂÂbrown to brownâÂÂsometimes darker centrallyâÂÂwith the stipe matching but lighter. A strong potassium hydroxide reaction turns fresh context bright yellow, fading with age or remaining only at the margin.
Microscopically, spores measure 10.9âÂÂ13.4 by 6.3âÂÂ7.5 micrometre (üm) and are amygdaloidâÂÂfusoid with a distinct suprahilar depression (the notch at the former point of attachment) and an elongated apex, much like those of Cortinarius collinitus. Their surfaces range from finely to moderately verrucose (warted) and stain slightly dextrinoid (reddishâÂÂbrown) in Melzer's reagent. Basidia are fourâÂÂspored, sand brown, 33âÂÂ45 by 8.5âÂÂ11 üm, bearing few dark granules. The lamellar trama consists of pale yellowish, smooth hyphae with small granules, while stipeâÂÂapex hyphae are pale brownâÂÂoutermost cells more reddishâÂÂwith scant dark granules. The pileipellis features a gelatinous epicutis of erectâÂÂsinuose hyphae typically 4âÂÂ6 üm wide over a repent layer of smooth, thinâÂÂwalled hyphae 5âÂÂ10 üm wide, spirally incrusted with angular dark redâÂÂbrown particles. Deeper hypodermal hyphae are slightly thicker, smooth to coarsely incrusted, containing dark redâÂÂbrown granular to farinose (mealâÂÂlike) contents.
Phlegmacium myrtilliphilum occurs in mesic spruceâÂÂdominated forests, where the understory ranges from richer to poorer bilberry (Vaccinium myrtillus) communities. At the time of its original publication, it had only been recorded in the middle boreal zone of Finland and Norway, suggesting it may be rare. Fruiting bodies emerge in autumn.