The main reason that fungi grow mushrooms is to produce and distribute their spores. These spores come in a variety of colors. Most spores are some shade of white, pink, brown or black There are also unusual spore colors like orange, yellow and green. In identifying boletes and gilled mushrooms, it can be very helpful to know the color of the mushroom’s spores. Since the individual spores are microscopic, to see their color without using a microscope you have to find or create a situation where there are many spores in the same place.
Sometimes this can be done by spotting a natural spore deposit on the mushroom or its surroundings; at other times you have to make a spore print, where you leave the mushroom on a piece of paper (or other medium) overnight. Another place where you find spores is on the gills of the mushrooms where they are created.
The simplest way to figure out a mushroom’s spore color is to look at the gills or pores. This is where the spores grow, so as more and more of them are produced, they change the gills (or pores) to their color. The photo above shows the color progression of the gills as a dark-spored mushroom matures. When it is young, its gills are white, as they are in many mushrooms, regardless of spore color. But as more and more of the spores mature, the gill color changes to a dark brown, which is closer and closer to the color of the spores.Here, the upper mushroom on the left has deposited its spores on the cap of the mushroom beneath it, so you can see the spore color directly. Note also the color of the gills of the mushroom on the right: they are in between the color of the spore deposit and the original white of the gills.
Natural spore deposits are not limited to those on other mushrooms. Here, this Gymnopilus has dusted its surroundings with orange-brown spores.
Boletes and spore color
With boletes, there are only a few situations where spore color gives you information that you wouldn’t get otherwise from the mushroom, and you usually get the spore color from the surface of the pores. For instance, some boletes in the genera Boletus and Tylopilus look very similar, but diverge as they mature. In this Tylopilus, the pore surface on the young mushrooms is pure white. But on the mature specimen at the top, the pores have turned a sort of brownish lilac, about halfway between that pure white and the pinkish brown spore color that is the key feature of Tylopilus:
If you can’t find a spore deposit on the mushroom itself, you may have to create the appropriate conditions yourself. If you remove the stem from a mushroom and leave it on a sheet of white paper overnight, the mushroom may leave a thick enough spore deposit on the paper that you can get an idea of the color. This is called making a spore print. Here is a set of spore prints made from a collection of local Agaricus mushrooms, which have a dark brown spore print:
I have also read in a few places that if your mushroom is dried up and doesn’t look like it will produce, putting a few drops of water on top of the cap may encourage it to sporulate. I’ve tried this several times and it has never worked.
Spore color and partial veilsNatural spore deposits can be quite subtle, and spotting them may depend on your species concept for the mushroom. For instance, this mushroom is a Cortinarius, a mushroom that has a wispy partial veil.
There are a few shreds of this partial veil clinging here and there to the edge of the cap, and to corresponding places on the stalk. These shreds have been colored brown by the discharged spores. At this point, you can also see that they match the gill color fairly closely.
Finding spore-colored shreds on the stem helps us form our species concept for the mushroom: not only do we now know the color of the spores, but we also know that this mushroom had a partial veil. In cases where the partial veil completely collapses against the stem, it can leave a smeary-looking spore-colored zone on the stem. This is called a ring zone, or an annular zone. The first photo on this page also shows annular zones on the stem.
Spores versus bruisingNote that when developing spores change the color of the gills, they do so gradually and smoothly. Here, a Cortinarius has purple gills originally, but they are gradually turning brown as its spores develop.
Gills also change color when they are cut or bruised. This may also be important for identifying the mushroom, but it does not indicate spore color. The color changes in the gills of this mushroom, for example, are the results of bruising or insect bites, not maturing spores.
One of the few special cases in this regard is the genus Panaeolus. This is a black-spored kind of mushroom whose spores mature unevenly on the gills, giving them a finely mottled appearance. Some other black-spored mushrooms can have this appearance as well.
Notice, however, that these gills are sort of evenly mottled throughout, showing that this is part of the natural development of the mushroom, not caused by a bruise or a localized insect attack. Note also the black annular zone on the stem, and the blackened shreds on the edge of the cap; these confirm what you would guess from the gill color: that this is a black-spored mushroom, and they also let you know that this mushroom started out with a partial veil.
Other kinds of mushrooms
Notice that I’ve only been discussing boletes and gilled mushrooms, and that almost all my examples are of gilled mushrooms. The distinction of Boletus vs Tylopilus is pretty much the only useful distinction that you can make among boletes by spore color, but even there (a) there are usually other ways you can get the same information and (b) most people collect boletes to eat, and by the time you can get a good spore print off a Boletus it’s usually too far-gone and wormy to eat. Spore color is also potentially helpful in identifying boletes in the genus Gyroporus (which has a bright yellow spore deposit) but the same issues apply: it’s simpler to just check for the hollow stem (another Gyroporus characteristic) and by the time they’ve deposited enough spores for a print, they’re usually too deteriorated to do anything with.
With the other mushrooms that you’re likely to come across – ascomycetes and polypores – the spore color isn’t generally helpful in determining their identity, and it can be difficult or impossible to obtain: ascomycetes generally release their spores in one puff at a time, and if you miss it you’re out of luck; polypores are so tough that they often remain on the tree for long after they’ve stopped producing spores, so a spore print is impossible.