Figure 1. A group of Tapinella atrotomentosa growing at the base of a conifer tree. (left) the cap color and size. (right) gills and brown folded margins.
Tapinella atrotomentosa is a saprotroph of conifers belonging to the Boletales order. It is often confused with Paxillus, but the two genera have different ecology. Paxillus is ectomychorizal and Tapinella is not. The cap can be large (10-15 cm wide) and is brown to orange with lighter margins. The cap rolls and has a brown margin. The stipe is thick and not hollow (3-4 cm) and can be brown to black, with a velvety feel. Gills are present, and usually close to medium spaced and white to brown. Can grow singly or in groups (Figure 1). Spore print is brown (Figure 3). When exposed to ammonia, the cap, stipe and gills first turn a bright purple, followed by green becoming black within a few minutes.
Figure 2. When exposed to ammonia (I used Windex®, which is an ammonia based cleaner) the cap, gills and stipe turn a bright purple (left) and become green then black (right).
Figure 3. Spore drop of Tapinella atrotomentosa.12.09.16