Some mushrooms are easy to identify because of their distinctive appearance. For example, the edible shaggy mane (Coprinus comatus) and the toxic fly agaric (Amanita muscaria) are hard to mistake for something else. On the other hand, many species look similar to one another or are variable enough that it is sometimes difficult to be sure what they are without a detailed examination. On top of that, the appearance of a particular individual mushroom is affected by the environment and stage of development, further complicating identification.
Using Spores in Mushroom Identification
If all mushroom spores looked alike, they wouldn't be much use in helping to distinguish one species from another. Fortunately for the mushroom hunter, there is a great diversity in the colors, and to some extent, the sizes and shapes of mushroom spores. The only way to analyze the size and shape of a spore is through microscopy. Determining spore color does not require a microscope. In fact, it is better to check the color without one.
What is a Spore Print?
Spore prints are made by collecting spores on a piece of paper. Mushrooms produce large numbers of spores. A fresh mushroom will continue to produce and release spores from its gills (or tubes in the case of boletes and relatives) for many hours after it has been picked. So many spores will be released, that they will form a pattern on a piece of paper placed under the cap, revealing their mass color.
How to Make a Spore Print
To make a spore print, cut off the caps of several small to medium sized mushrooms that have developed to the point that their gills or tubes are fully exposed. The fresher the mushrooms the better. Place the caps on a white sheet of paper out of direct sunlight. Keep the caps away from open windows, fans, air conditioners, or other sources of moving air. Not only will this keep most of the spores on the paper, but it will reduce drying which will allow the cap to release spores for a longer time.
Let the caps remain on the paper for at least an hour or two. It is okay to lift the caps to check for a spore print, but to produce an attractive gill-shaped deposit, the caps should be undisturbed until enough have been ejected to be easily visible. Often this will take several hours. Sometimes it takes overnight.
When the spore print is "done," spores will be plainly visible on the paper. One exception is if the spores are some shade of white. Even so, if the print is allowed to develop long enough, even spores that are virtually the same color as the paper will be visible. It is important to use only white paper. This is because the perception of the actual color of the spores is influenced by the background color, so all spore print conditions should be kept the same as much as possible to have a consistent color reference frame.
Some people suggest taking prints of light colored spores on black paper, but it is really not necessary, unless the mushroom is not producing many spores, in which case a light deposit may be more easily seen on the darker color.
Special Spore Print Techniques
Sometimes the only specimen on hand is in poor condition. It may be quite dry, too wet, or decomposing. Wet dry caps with enough water (use a dropper) to fully rehydrate them. Depending on the size of the cap, only a few or several dozen drops is enough. This will usually start the cap sporulating enough to get a good spore print.
If a cap is unusually small, or in really bad condition, it can help to elevate it above the surface of the paper. A rotting mushroom will stain the paper, and discolor it to make the true spore color more difficult to determine. For these situations, pierce a small clear plastic container through the bottom with a pin, and suspend the cap on the end of the pin point a few millimeters above the paper. This prevents staining of the paper, and creates a still-air environment around the cap.
Spores come in a beautiful array of colors ranging from pure white and cream, to shades of pink, red, brown, purple, green and black. Spore color is usually enough to at least place the mushroom in the proper genus, even if it can't be identified all the way to the species level. Just as importantly, it rules out a lot of species that the mushroom definitely cannot be.
Philip McIntosh - The author holds a B.Sc. in Botany and Chemistry and an M.A in Biology and he has thirty + years of experience in science and industry.
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