Cortinarius bovinaster is an rare agaric fungus in the family Cortinariaceae. Described as a new species in 2013, it is only found in boreal and hemiboreal zones of Finland and Sweden.
Cortinarius bovinaster produces a slender fruit body with a cap 1.5âÂÂ8 cm across. When young, the cap is broadly conical to hemispherical and matures to a low, flattened dome often marked by a shallow central bump (umbo. Its surface is clothed in fine fibres (fibrillose) and appears brown to greyâÂÂbrown when moist, fading to a pale yellowishâÂÂbrown as it dries (hygrophanous). The gills beneath the cap are spaced moderately to rather distantly and feature a slight notch where they join the stipe (emarginate attachment); they start pale yellowishâÂÂbrown and darken to deep brown as spores develop. The stipe itself reaches 3.5âÂÂ9 cm in height and is up to 1 cm thick at the top, tapering only slightly towards a broader base. It is initially covered in whitish fibrils that soon turn greyishâÂÂbrown with handling. Traces of the universal veil may persist as a delicate, whitish sheath or ring low on the stipe. The flesh is uniformly pale greyâÂÂbrown, becoming darker towards the base, and yields no distinctive odour when cut.
Under the microscope, the spores measure 8.8âÂÂ10.7 by 5.4âÂÂ6.3 üm (average 9.2âÂÂ9.9 by 5.7âÂÂ6.0 üm) and are narrowly ellipsoid to tearâÂÂshaped. Their surface bears fine, densely packed warts (verrucose ornamentation), and they stain a reddishâÂÂbrown in Melzer's reagent (dextrinoid reaction), reflecting their characteristic wall chemistry. The gill tissue (trama) is composed of hyphae that are smooth to very slightly roughened, while the cap cuticle (pileipellis) consists of thinâÂÂwalled hyphaeâÂÂmostly smooth but occasionally showing fine scabrous patches. Clamp connections (small hookâÂÂlike bridges between hyphal cells) are present throughout the mushroom's tissues, a feature typical of this group.
Cortinarius bovinaster fruits from midâÂÂAugust to early September in mesic to fairly damp coniferous woodlands (comprising principally Picea abies or Pinus sylvestris) on calcareous soils. It is known to occur in the boreal and hemiboreal zones of Finland and Sweden, where it is rare. In the 2019 Finnish red list, Cortinarius bovinaster is considered a near-threatened species, unchanged from its 2010 classification.