The Mustard Yellow Polypore (Fuscoporia gilva) is a common decomposer of broadleaf wood that can be found year-round, but shows its most vivid colors during wet periods in the summer when it is actively growing. It is widely distributed in North America.

The cap surface color is reddish to yellow-mustard when young, becoming darker, then black with age. The fertile structure (hymenopore) color is similar or darker. The hymenopore consists of tiny pores.

This mushroom is easy to distinguish using drops KOH (black) and ammonia (darkening).

The inner flesh (context) is a yellow-mustard color and can be sometimes observed even when the mushroom is old and has turned black with age.

September 7th, 2023 Field Notes - Indian Cave State Park

Shelving gregariously on fallen Ash tree in open interface between riparian and mixed oak/hickory woodland areas.

• Caps thin with concentric zonation, brown with an orange-brown margin.
• Hymenophore finely poroid, primarily brown and orange-brown near margin.

Additional Info

• KOH blackish on all surfaces.
• Ammonia dark on all surfaces.