Stereum hirsutum is a hardwood-loving crust fungus that is often confused with Trametes versicolor (Turkey Tail). It is classified as: Basidiomycota > Agaricomycetes > Russulales > Stereaceae > Stereum > hirsutum.
It develops medium-sized cap structures that often fuse laterally with one another. It is smaller and more frequently fused than S. ostrea, larger and less orange than S. complicatum, and does not “bleed” red latex like several other Stereum spp. The name S. hirsutum is generally applied by mycologists to a group of species that blend into one another, as the forms “are defined by external morphological features, and these are not dependable” (Welden 1971). Stereum studiers might say that S. hirsutum, S. complicatum, and S. gausapatum are along a continuum, and not as distinct as some guides might claim.
S. hirsutum are saprobic on dead wood of hardwoods, especially oaks. They grow densely from gaps in bark, and then fuse together laterally, causing a white rot of the heartwood. This can often serve as a host to algae, and it even sometimes parasitized by jelly fungi. The fungus is prevalent throughout all seasons of the year and is very widely distributed throughout North America.
The fruiting bodies are individually 0.5-3cm across, but are usually fused together. These groups are fan-shaped, semicircular or irregular, densely velvety, and hairy. There are concentric zones of texture and color, with colors variable but generally yellow to tan or reddish brown. Sometimes, they develop green tinges as they age, due to algae colonization. The fruiting bodies don’t have a stem, and the undersurface is smooth, yellow-brown or gray.
It dyes red in KOH, and sometimes turns black. The spore print is white and difficult to obtain. Spores are 5-8 x 2-3.5um, smooth, cylindric or narrowly elliptical, and amyloid. Under the microscope, one can see hyphidia that are plain, without projections or spikes.