Mushroom Spore Print: How to Make One and Read It

A mushroom spore print is the powder that falls from the gills or pores when a cap sits undisturbed on a surface. This is the method the North American Mycological Association (NAMA) teaches:

• Cut the stem off a mature cap. If you do not know what the mushroom is, wear gloves or wash your hands afterwards.
• Lay the cap gills-down (or pores-down) on white paper, an index card, aluminium foil or a glass slide.
• Put a drop of water on top of the cap to help it release spores.
• Cover it with a cup, glass or bowl so air currents do not scatter the spores.
• Leave it for 2 to 24 hours. NAMA says the time depends on humidity and on how fresh the mushroom is.
• Lift the cap straight up and look at the deposit in daylight.

NAMA also describes a hanging version: punch a hole in an index card, rest the card on a cup and push the stem through so the cap sits on the card. Wikipedia notes that mycologists often print onto glass slides so the spores can go straight under a microscope.

White and cream prints disappear on white paper. The Beaty Biodiversity Museum at the University of British Columbia suggests dark paper for mushrooms with light gills, light paper for dark gills, and a sheet that is half white and half dark when you cannot guess. Foil and glass work for both, because you can hold them against a white or a dark background afterwards.

The thickness of the deposit changes the colour you see. Wikipedia gives the example of Lactarius, whose thin deposits look white while thick ones look cream to yellow, so judge the colour where the print is heaviest.

Spore colour sorts mushrooms into groups, usually at genus level. The groups below come from MushroomExpert.com's key to dark-spored gilled mushrooms and from Wikipedia.

• White to cream. Amanita, including the death cap, the destroying angel and the fly agaric; Wikipedia says the genus prints white and accounts for 95% of deaths from mushroom poisoning. Clitocybe, such as the ivory funnel, prints white, off-white, buff, cream, pink or light yellow (Wikipedia). A white print does not mean harmless.
• Salmon pink. Entoloma (Wikipedia). Wikipedia describes the print of the livid pinkgill as reddish-brown, so the pink group can look darker than its name.
• Brown to yellowish brown. Agrocybe, Bolbitius and Inocybe (MushroomExpert.com).
• Rusty or cinnamon brown. Cortinarius, Conocybe and Pholiotina, Galerina, Gymnopilus and Hebeloma (MushroomExpert.com). This group includes the funeral bell and the fool's conecap, which both carry amatoxins.
• Chocolate brown. Agaricus (MushroomExpert.com).
• Purple-brown to black. Hypholoma such as sulphur tuft, Stropharia and Psilocybe, and the ink caps such as the common ink cap (MushroomExpert.com). NAMA notes that the shaggy ink cap drops a surprising amount of black spores.
• Green. Chlorophyllum molybdites, the green-spored parasol, which Wikipedia calls the only large mushroom with a green spore print.
• Olive or greyish. Gomphidius and Chroogomphus (MushroomExpert.com).

Boletes and other mushrooms with pores instead of gills print the same way, pores down. For hard bracket fungi, NAMA suggests wrapping the specimen in wet paper towels overnight before printing so that it starts releasing spores.

Puffballs and earthballs have no gills or pores; their spores form inside. The Beaty Museum notes that for these closed fungi you may need to cut the fruiting body open and look at the colour of the spore mass itself. For a white ball found in a lawn, the cut is the more important check anyway: see white ball mushroom in yard.

• Too young or too old. Wikipedia notes that some specimens are too immature or too old to drop spores.
• Too dry. Add the drop of water NAMA recommends and keep the cap covered.
• Not long enough. Give it the full 24 hours before deciding nothing is coming.
• Moved down from the mountains. Wikipedia reports that specimens collected at high elevations often fail to print when brought down to lower ground.
• A print that does not match the books. The naturalist behind Backyard Nature reports getting pale grey prints from specimens identified as Chlorophyllum molybdites, a mushroom normally described as printing green. Repeat the print with a more mature cap before relying on the colour, and never treat an unexpected colour as a sign that a mushroom is harmless.

NAMA suggests spraying a finished print lightly with artist's fixative or hairspray, holding the can at least 12 to 15 inches above it so the spray does not blow the spores away. PBS Utah's spore-print art project puts wild mushroom caps on white or grey paper inside a closed clear container for 24 hours, and notes that store-bought mushrooms did not work for the craft. Children should collect mushrooms only with an adult present, and nobody should eat a mushroom used for a print.

For ordinary mushrooms, yes: a spore print is a normal identification step taught by mycological societies. The legal question is about the spores of psilocybin ('magic') mushrooms. Wikipedia's article on the legal status of psilocybin mushrooms says their spores contain no psychoactive chemicals, that they are explicitly illegal in Georgia, Idaho and California, and that elsewhere in the United States selling spores for the purpose of growing hallucinogenic mushrooms is illegal. State laws change, so check the current law where you live. This site does not help with growing psilocybin mushrooms.

Wikipedia is explicit that a mushroom cannot be identified from its spore print alone; the print is one feature among several. Combine it with the stem base (dig it out and look for a cup-like volva), how the gills attach, the cap surface, smell, any colour change when cut, and what the mushroom grew on. Then photograph the mushroom and its print together and check them with the app or an expert. No combination of these features tells you a wild mushroom is safe to eat. If anyone has eaten one, call Poison Control at 1-800-222-1222 (U.S.) right away.