A spore print is the deposit left when a mature mushroom cap drops its spores onto the surface beneath it. A single cap can release many millions of spores, and they fall in the pattern of the gills or pores, leaving a negative image of the underside.
Its value is the colour. Spore colour is one of the most reliable characters for placing a gilled mushroom in the right genus, and it is something no photograph can tell you.
A mature mushroom with the gills or pores exposed, ideally with any veil already broken. A sheet of paper that is half white and half black, or a piece of glass or foil. A bowl or glass to cover the cap. That is all. For practice, a shop-bought chestnut or oyster mushroom works perfectly well.
Paper is best for reading colour, and half-black, half-white paper shows pale and dark prints equally well. Foil is cleaner and folds into a sealed packet, which is why it is the usual choice for storing prints. Glass is ideal for microscopy: a print on a slide can be scraped straight into a drop of water under a cover slip.
| Print colour | Typical genera |
|---|---|
| White to cream | Amanita, Lepiota, Pleurotus (oyster), Hericium (lion's mane), Tricholoma, most Russula and Lactarius |
| Pink to salmon | Pluteus, Entoloma, Volvariella |
| Rust to ochre brown | Cortinarius, Galerina, Gymnopilus |
| Chocolate brown | Agaricus (field and button mushrooms), Agrocybe |
| Purple-brown | Psilocybe, Hypholoma, Stropharia |
| Black | Panaeolus, Coprinopsis and the ink caps |
Two warnings belong next to any chart like this. Colour narrows a mushroom to a group of genera; it does not identify a species. And some of the most dangerous fungi in Britain, the death cap and destroying angel among them, print white, while Galerina marginata, which carries the same toxins, prints rust-brown. Never eat a wild mushroom on the strength of a spore print. Our journal article on what spore print colour tells you goes further into the chemistry of spore pigment.
Scrape a little of the print into a drop of water on a clean slide, lower a cover slip over it and survey at 400x. To measure, move to 1000x with oil and calibrate against a stage micrometer. Our guides to magnification and to viewing spores cover the technique, and the microscopy kit page lists the equipment.
Dry, dark and cool. A sealed foil packet or a clean zip bag in a drawer keeps a well-dried print far longer than a spore suspension lasts, which is why prints are the archive format of choice for herbaria and reference collections. Label every print the day you make it; an unlabelled print is a mystery within a month.