Pholiota / Yellow-Cap Fungus

Pholiota spp.

Host(s) in Alaska:

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

Habitat(s): stem and root decay

Current Status & Distribution in Alaska (2023 Update)

Pholiota spp. were detected at 16 locations during ground detection surveys in 2023. Observations were made near Anchorage and on the central Kenai Peninsula in Southcentral Alaska and around Fairbanks and Healy in Interior Alaska. Of these detections, seven were on Alaska birch, six on aspen, and one each on white spruce, balsam poplar, and mountain hemlock. Many Pholiota occurrences have been mapped on aspen, birch, black spruce, and willow in Southcentral and Interior Alaska (see Detection Map) but most have not been identified to species. 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. Mushrooms collected from  live Sitka spruce and western hemlock trees near Juneau were molecularly confirmed to be Pholiota (99% sequence match to Pholiota aurivella) in 2020. Pholiota is generally less frequently encountered in Southeast Alaska than other parts of the state, though eight research grade observations were submitted via iNaturalist in in Skagway, Juneau, Sitka and Ketchikan. Three research grade records came from Fairbanks, Denali Park and Talkeetna.

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

Georeferenced observations of Pholiota spp. in Alaska as of 2023 with
the distribution of known hosts. Modeled host tree distributions were
developed by the Forest Health Assessment and Applied Sciences Team
(formerly 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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