Fungi are divided into several major phyla, with Ascomycota and Basidiomycota being the most familiar to foragers. Basidiomycota contains most of the classic mushrooms, including gilled agarics, polypores, and boletes, all of which produce spores on club-shaped cells called basidia. Ascomycota, on the other hand, includes morels, truffles, yeasts, and many molds, and produces spores inside sac-like cells called asci. Other phyla, including Zygomycota, Chytridiomycota, and Glomeromycota, contain molds, aquatic fungi, and important mycorrhizal partners, respectively. Beyond this taxonomic structure, mushrooms can be grouped by their shape and spore-bearing surface.
Gilled mushrooms, known collectively as agarics, make up the largest and most familiar group. Boletes have pores instead of gills, giving them a sponge-like feel, and include prized edibles like the porcini (Boletus edulis, also called the king bolete). Polypores are often woody and shelf-like, growing on trees rather than soil. Chanterelles have forked, blunt false gills running down their stems and a fruity aroma, while true morels display a distinctive honeycomb texture. Truffles are underground ascomycetes whose strong aroma is detected by trained dogs or pigs. Puffballs are round mushrooms that release a cloud of spores when mature; the rule for eating puffballs is to slice them open and consume only those with a uniformly white interior. Other distinct forms include stinkhorns, which smell foul to attract flies, coral fungi with their branching, coral-like shapes, oyster mushrooms (Pleurotus) that grow in shelf clusters on wood, and hedgehog mushrooms (Hydnum repandum) recognized by their tooth-like undersides.
Accurate identification relies on combining multiple clues. The four key steps are habitat, gross morphology, spore print, and microscopic features when needed. A dichotomous key walks the forager through paired questions until a species is identified, while a good regional field guide and cross-referencing among multiple sources reduces errors. Distinctive smells (almond, anise, cucumber) can be diagnostic for some species, and techniques like the bruising test, in which the flesh is scratched to observe any color change, or the KOH test, in which potassium hydroxide is applied to provoke a color reaction, provide additional clues. A microscope reveals spore shape and other fine details. Photographing the habitat is also valuable, because many mushrooms associate with particular trees or substrates, and that information can be crucial later when confirming an identification. Even the so-called easy edible species require several confirmations before eating.