Identification of mushrooms can be very difficult. Mushrooms are not like birds or wildflowers, where everything you see was described and named some time ago. In fact, there are large groups of fairly common mushrooms in the United States where most of the species are still undescribed. So if you really need to have names stuck on everything you find, mushrooming may be a frustrating pastime; on the other hand, if you like finding scientifically unknown things, and maybe helping to figure out what they are, then mushrooming is the pastime for you!
If you have a "mushroom-shaped" mushroom, your first step in identifying it is to determine its spore color. If your mushroom is not "mushroom-shaped" (for example, a coral fungus, morel, or polypore), identification is more dependent on the shape of the fruiting body and microscopic features.
The classic way to find out a mushroom's spore color is to take a spore print: place the mushroom's cap on a piece of paper or aluminum foil with the gills or pores facing downwards. It sometimes helps things along if you paint the cap with a drop or two of water. Leave the cap there for a few hours, or overnight. Sometimes (especially if the cap is small) it helps to put a cup or bowl over the cap, so that stray air currents don't blow the spores away. After a while, unless your mushroom is too far gone, enough spores will be deposited on the paper (or aluminum foil) to make a pattern that looks like the hymenophore of the mushroom. The color of this pattern is the spore color of the mushroom.
Sometimes the mushroom will help you out by depositing enough of its spores on its surroundings (or on the lower mushrooms in a cluster of them) that you can tell the spore color right away - - the mushroom has made a natural spore print for you.
In this case, a Ganoderma applanatum has deposited its brown spores all over the vicinity.
The base of the stalk turns out to have all sorts of useful features for identification. It is essential to dig the mushroom up carefully if you don't know what it is.
For one thing, the mushroom may have a rooting base, or rhizomorphs, and you won't see these if you just break it off. For another, the mushroom may have a fragile volva or universal veil fragments around the base, and these may be lost if you're not careful in collecting it.
Another important features is the mushroom's habitat: is it growing on the ground, on wood, or something else? If it is growing on the ground, it is often important to note what trees are growing nearby. Some mushrooms are symbiotic with trees, and only grow with certain particular ones.
How do the gills meet the stalk? As I've built the key for this website, this feature has turned out not to be terribly important, but is still used sometimes to help identify things to the genus level.
Check to see if your mushroom has/had a partial or universal veil. Don't just look for the obvious signs: a ring on the stalk or a cup at the base. Look for shreds or patches or velar material on the stalk, cap, or hanging from the capmargin. See the entries on veils for more help.
One last, important word about cap color: unlike flowers, but like just about everything else, mushrooms fade in the sunlight. The diagnoses here often include the mushroom's "faded" color, but not always. You may have to decide at some points that the dull pink on your specimen was once an intense red.
Rain also plays havoc with mushroom identification. It can wash out cap color just as effectively as sunlight, and it can also wash off all sorts of flakes and scales that are important for identification. If your mushroom has been rained on, you'll probably have a much tougher time identifying it.
