Ganoderma is a genus of polypore fungi in the family Ganodermataceae that includes about 80 species, many from tropical regions. They have a high genetic diversity and are used in traditional Asian medicines. Ganoderma can be differentiated from other polypores because they have a double-walled basidiospore. They may be called shelf mushrooms or bracket fungi. The genus Ganoderma contains polypores that feature distinctive, double-walled, chambered-looking spores (see the illustration to the right). Without a microscope, one group of Ganoderma species is fairly easy to recognize, featuring “laccate” (shellacked or lacquered-looking) caps. The second group of Ganoderma species is a little less easily separated from other polypores without a microscope, although this group does contain the well-known “artist’s fungus,” Ganoderma applanatum; in this group the caps are dull brown. In both groups the pore surfaces bruise brown (sometimes slowly), and the flesh turns black with KOH. Species of Ganoderma are parasitic and saprobic on the wood of hardwoods or conifers, and are relatively picky about their substrate, rarely crossing the hardwood/conifer line and sometimes limiting themselves to certain trees. Ganoderma identification relies on many characters that are accessible without recourse to microscopic work, although measuring spores is also sometimes informative. The color of the flesh, when dried, ranges from white to pale brown to dark brown, and picking one of these three colors is important. In some species the flesh features “concentric growth zones” (illustration), which can be seen as textural zonations when the surface has been sliced cleanly with a razor blade (a magnifying glass will help in assessing this feature). Another feature of the flesh in some Ganoderma species is the presence of “melanoid bands” (illustration), which are blackish, sub-shiny bands that, like the concentric growth zones, may be difficult to spot without a cleanly-cut edge and a magnifying glass. Other useful features in Ganoderma identification include the presence or absence of a stem, the kind of wood the mushroom is growing on, and the known ranges of the species. However, the stem (or pseudostem, or not-stem) is in my experience a very unreliable character, since species frequently develop stems when they’re not “supposed to,” and neglect to develop them when they “should.” The North American species of Ganoderma have been confused and confusing for decades—especially the shellacked species. But recent publications by Loyd and collaborators (2017, 2018) have studied hundreds of North American collections and focused the picture substantially.
