Forest & Grassland Health

Pholiota / Yellow-Cap Fungus

Pholiota spp.

Host(s) in Alaska:

aspen, birch, cottonwood; less frequently, spruce and hemlock

Habitat(s): stem and root decay

Photos

Click image for larger version.

Pholiota mushrooms from pocket guide. Pholiota on live Sitka spruce near Juneau. Pholiota mushrooms in Valemont, BC. Black and white photo of Pholiota.  

Pholiota spp. mushrooms.

Pholiota spp. mushrooms on a wounded, live Sitka spruce in Southeast Alaska.

Pholiota spp. mushrooms in Valemont, B.C.

Pholiota spp. mushrooms at the base of an aspen tree.

 

Current Status & Distribution in Alaska (2020 Update)

In 2020, one record of Pholiota was documented on birch  in Denali State Park. To date, many Pholiota occurrences have been mapped on aspen, birch, black spruce, and willow in Southcentral and Interior Alaska (see Map) but most have not been identified to species. Many Pholiota citizen science observations were made in 2020 in iNaturalist. At least ten observations appeared to correctly identify the genus, but even some of the observations labeled as research grade were likely erroneous (in that they were identified to species when true identification can be challenging and/or require molecular tools); unfortunately, the records seldom include host tree information, which can aid in identification. Pholiota mushrooms are most common at the base of trembling aspen, but usually these trees have no symptoms until they uproot or snap near the root collar. Last year, mushrooms found on a live Sitka spruce and a western hemlock tree near Juneau were molecularly confirmed as Pholiota (99% sequence match to Pholiota aurivella). Pholiota is less frequently encountered in Southeast Alaska than other parts of the state.

Identification & Injury (from Insects & Diseases of Alaskan Forests book)

The fruiting body is an annual mushroom, typically produced in clusters. The fungus is called the yellow-cap fungus or the scaly-cap mushroom. The upper surface of the mushroom cap is yellow-brown and usually scaly and/or sticky. Young specimens may be flagrantly scaly while older specimens may become sticky and lose their scales. Gills on the lower surface are yellow at first, later turning brown. The stem (i.e., stipe) may or may not have a ring and may be scaly. Mushrooms may develop at the base of the tree or on the stem, particularly at wounds. Incipient wood decay appears as light yellowish areas in the heartwood. Wood with advanced decay is yellow-white with yellow or yellow-brown streaks. Thin strands of yellow-brown mycelium, occur along the grain. If the strands of mycelium are pulled from the wood, irregular channels, resembling insect tunnels, remain.

Pholiota species cause a white rot of wood in live trees, typically invading through wounds. Mushrooms on a living tree indicate extensive decay. Some species are root rot fungi while others cause stem decay. Several Pholiota species have been reported to cause butt and trunk rot of trembling aspen throughout its range in North America. There are many species of Pholiota found in Alaska, only some are capable of decaying live trees. For exact determination of any specific specimen, a key for Pholiota must be used (available here). Managers can reduce effects of wood decay fungi by limiting tree ages through shorter rotations and by reducing trunk wounds. 

Detection Map & Host Distributions

Observations of Pholiota spp. in Alaska as of 2020.

Georeferenced observations of Pholiota spp. in Alaska as of 2020 with the distribution of known hosts. Modeled host tree distributions were developed by the Forest Health Technology Enterprise Team in 2011 (240m-resolution, presence based on dominant tree species by tree diameter).

 

Links & Resources

Smith, Alexander H.; Hesler, L. R. 1968. The North American species of Pholiota. New York, NY: Hafner Publishing Company. 349 p. Available here.

 

Content prepared by Robin Mulvey, Forest Health Protection, robin.mulvey@usda.gov.

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