What You Should Know
Paxillus Atrotomentosus is an inedible large agaric that has a brown cap, buff gills, and a dark brown, velvety, sometimes eccentric stem. The mushroom grows in woods and three stands, on and around conifer stumps and sometimes buried, coniferous wood.
The blackish-brown wooly stipe distinguishes this mushroom from other species of Paxillus.
Formerly grouped with the mycorrhizal rollrims such as Paxillus involutus, the Velvet Rollrim bore the name Paxillus atrotomentosus; however, it is now known to be a saprobic fungus (a wood rotter) and only distantly related to Paxillus species. Since 1992 it has been sited in a separate genus.
Other names: Tapinella atrotomentosa, Velvet Rollrim, Velvet Paxillus, Velvet-footed Pax.
Tapinella atrotomentosa Mushroom Identification
Saprobic; growing alone or in groups, sometimes in clusters, on conifer stumps, decaying conifer wood, or on living conifers - also reported on the wood of madrone; causing a brown rot; summer and fall; widely distributed in northern North America and the Appalachian Mountains.
5-14 cm; broadly convex, becoming flat or shallowly vase-shaped; dry; densely to finely velvety; brownish yellow to yellow-brown or reddish-brown when young; usually becoming darker brown in age, but sometimes retaining a yellowish margin; the margin inrolled at first, often becoming widely scalloped in old age.
Running down the stem; separable as a layer; close or crowded; short-gills frequent; whitish when young, becoming pale tan or yellowish; frequently forked or with cross-veins near the stem.
4-10 cm long; 2-5 cm thick; equal, or swollen in the middle; occasionally off-central or even lateral; thick and sturdy; dry; whitish near the apex, but covered with velvety brown to blackish brown fuzz below.
Thick and firm; whitish to yellowish.
Ammonia bright purple on cap and stem surfaces. KOH black--or flashing green, then resolving to greenish-black - on cap and stem surfaces; dirty olive on flesh. Iron salts negative on cap and stem surfaces.
Yellowish-brown to brownish-yellow.
Spores 4-6 x 3-4 µ; ellipsoid; smooth; hyaline in KOH; dextrinoid. Hymenial cystidia not found. Pileipellis a tangle of brownish-in-KOH elements 2.5-5 µ wide; terminal cells cylindric-tubular with rounded to subacute apices, bundled in upright aggregations.
Tapinella atrotomentosa Edibility
Although Tapinella atrotomentosa mushrooms are not generally considered edible, they have been used as a food source in parts of eastern Europe. Tests on the chemical composition and free amino acid levels of the mushroom suggest that they are not considerably different from other edible gilled mushrooms such as Armillaria mellea.
Linus Zeitlmayr reports that young mushrooms are edible, but warns that older ones have a foul bitter or inky flavor and are possibly poisonous. The bitter flavor is allegedly improved by boiling the mushrooms and discarding the water but is indigestible to many. There have been cases of poisoning reported in European literature.
Tapinella atrotomentosa Taxonomy and Etymology
This mushroom was originally described in 1786 by the German naturalist August Johann Georg Karl Batsch (1761 - 1802), who named it Agaricus atrotomentosus.
The Velvet Rollrim was transferred to the genus Tapinella in 1992 by the Czech mycologist Josef Šutara (born 1943), who renamed it Tapinella atrotomentosa.
Synonyms of Tapinella atrotomentosa include Agaricus atrotomentosus Batsch, Paxillus atrotomentosus (Batsch) Pers., Rhymovis atrotomentosa (Batsch) Rabenh., and Sarcopaxillus atrotomentosus (Batsch) Z. Malysheva & E.F. Malysheva.
Tapinella as a mushroom genus was circumscribed in 1931 by the French mycologist Jean-Edouard Gilbert (1888 - 1954).Tapinella comes from Tapis, meaning a carpet. The specific epithet atrotomentosa is much more straigtforward. It comes from the Latin prefix atro- meaning black, and tomentosa meaning covered in short, dense, matted hairs - a reference to the distinctive surface of the stems of Velvet Rollrims, which are black and tomentose (velvety).
Tapinella atrotomentosa Chemistry
Tapinella atrotomentosa has a wound-activated defense mechanism whereby injured fruit bodies convert chemicals known as leucomentins into atromentin, butenolide, and the feeding deterrent osmundalactone. Atromentin had previously been identified as the pigment-producing brown color of the cap but was not characterized as a chemical defense compound until 1989. Other compounds produced by the fungus include the orange-yellow flavomentins and violet spiromentin pigments. A novel dimeric lactone, bis-osumundalactone, was isolated from the variety bambusinus.
Several phytoecdysteroids (compounds related to the insect molting hormone ecdysteroid) have been identified from the fungus, including paxillosterone, 20,22-p-hydroxybenzylidene acetal, atrotosterones A, B, and C, and 25-hydroxyatrotosterones A and B.
Photo 1 - Author: Holger Krisp (Creative Commons Attribution 3.0 Unported)
Photo 2 - Author: Robert Flogaus-Faust (Creative Commons Attribution 4.0 International)
Photo 3 - Author: Björn S. (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 4 - Author: Syrio (Creative Commons Attribution-Share Alike 4.0 International)
Photo 5 - Author: Dr. Hans-Günter Wagner (Creative Commons Attribution-Share Alike 2.0 Generic)
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