Paxillus cuprinus

What You Should Know

Paxillus cuprinus is a toxic mushroom with a depressing brown cap. It grows under silver birch trees and turns brown when damaged.

The name Paxillus involutus has been used for at least three different Paxillus species of western North America. As a result of the taxonomic confusion, the range extent and habitat of each species are unclear. The poison pax, Paxillus involutus, is widespread in temperate and boreal Europe and barcode sequencing shows that it occurs in BC.

Paxillus cuprinus Mushroom Identification

1. Cap

   5-12 cm diameter, convex when young then expanded and flattened with slightly depressed center, more deeply depressed in older specimens, without an umbo (raised area in the middle), margin strongly inrolled when young, later weakly or not inrolled; the surface has a faint whitish dusty coating on very young specimens, felted and matt when young, slightly sticky in wet weather, smooth and shiny when dry and with age, often cracking when dry; surface color gray-brown with an olivaceous shade, soon becoming ochraceous brown, clay-buff or yellowish olivaceous, finally more uniformly coppery brown or reddish-brown, rarely with a vinaceous cast.

2. Gills

   Unequal, narrow, fairly crowded to crowded, decurrent, often forked, branched and joining towards the stem; color at first pale, yellowish-white then rusty brown darkening to rusty reddish or reddish coppery with age, staining red-brown when bruised.

3. Stem

   2.7-5 x 0.5-2.5 cm, stout but sometimes more slender to thin, dry; whitish background color, more or less pale pink reddish marbled, often with a distinct light yellow zone at the top, staining reddish brown from the base upward later with brown striations. Flesh: yellowish in the stem and the cap reddish-brown to dark-red after a few hours.

4. Chemical reaction

   Reddish-brown to purplish brown with 50% ammonia solution on cap surface.

5. Spore Print

   Ochraceous with clearly reddish shade or chocolate brown turning to ochraceous-olivaceous brown over time.

6. Spores

   (7.0)7.2-9.6(11.5) x (4.5) 4.8-5.9(6.2) μm with median 8.0-8.6 x 5.2-5.5 μm. Smooth, ellipsoid-ovoid to amygdaliform with a constant to frequent apical constriction.

7. Similar Species

   Paxillus cuprinus, the coppery pax, is common in parks and lawns growing with planted birch (Betula) from California to BC. Two other species grow in natural habitats, but their names and identities have yet to be sorted out. They differ in subtle macroscopic and microscopic characters from each other. All Paxillus species are considered toxic.

Sources:

Photo 1 - Author: Lukas from London, England (Creative Commons Attribution-Share Alike 2.0 Generic)

Photo 2 - Author: Lukas from London, England (Creative Commons Attribution-Share Alike 2.0 Generic)

Photo 3 - Author: Lukas from London, England (Creative Commons Attribution-Share Alike 2.0 Generic)