Boletes are basidiomycete mushrooms that at first glance look like normal gilled mushrooms but instead use pores (or sometimes "tubes") on their undersides to distribute spores. They're sometimes called "sponge fungi" or "fleshy fungi" because of this and their high moisture content. Boletes are quite a diverse and sometimes beautiful bunch along with being relatively safe to consume. At the very least, you'll never find a species that'll kill you like the destroying angels, death cap or the deadly galerina.
With bolete season, typically mid-July up until the end of autumn here in New England, coming up for some of us now is a wonderful to go collecting mushrooms for the table. Four simple rules to follow will ensure that even begining mycophagists will not spend the next two days paying tribute to the porcelain goddess and will only cut a moderate portion of the edible boletes out.
- Eat only young, fresh specimens. This is an easy rule to follow, and important for two reasons. First, you wouldn't want to get food poisoning or digest too many insects or insect waste. Boletes are a favorite of insects, so expect to find them and some larval trails. This shouldn't be a problem if you cut them out and cook the mushroom. Second, while most boletes will keep their color the undersides of some will darken with age, so you'll want to be wary as this will obscure some important identifing macrofeatures.
- Don't eat boletes with red or orange pore sufaces. This is important in avoiding certain poisonous species such as Boletus satanas.
- Avoid boletes that bruse blue or green. This unfortunately takes out a good deal of boletes, but is important in avoiding other poisonous or undetermined species.
- Avoid the orange-capped species in the genus Leccinum. Most people won't have a problem with these and guides (mine included) will typically label these as edible, but some people experience stomach upset from these. I've never tasted one, but they're reported to be quite good. If you want to try one, try to identify it to species (rather difficult with Leccinum) and take a small bite to see how your digestive system reacts.
Of course, there is always a very small risk of running into a new species that could be poisonous. For that reason, it might not be a bad idea to try a small, cooked sample and wait 24-48 hours before gorging yourself. You also might want to try to get an idea of the genus and species of the bolete in question. If you're lacking a good field guide, you can check out the keys available at MushroomExpert.com or Harry Thier's guide The Boletes of California. Both can be accessed at the URLs below:
Boletes are typically larger than their gilled cousins and may reach up to 15 cm or more in diameter. They're typically bulbous or convex when young and will become flat or flattened and convex as they age. They tend to rot quicker than most other mushrooms and are most often found sprouting from the ground. The great majority of boletes are mycorrhizal and some are very selective about the trees they associate with. Unlike Polypores, their tubes are easily removable from the cap, and their length can be very shallow or more than a centimeter deep. These tubes are lined with the fertile layer known as the "hymenium", which contains the cells called the basidia. The basidia typically bear up to four basidiospores, which is how all Basidiomycetes reproduce. These basidiospores will fall through the tubes by succumbing to gravity and will continue the species by finding new substrates to colonize.
When you want to identify a bolete to genus and species, there are a few things you should look out for. Unlike identifing other kinds of mushroom, color of features is an important and consistent macrofeature of boletes. You should pay attention to what color the bolete will bruise on the cap, pore surface, and stem. You can do this easily by depressing a knife on a fresh specimen and waiting 30 minutes for a change. Beware when doing a spore print of boletes, as some insects will lay eggs that will hatch overnight in mushroom's flesh.
George Barron. Mushrooms of Northeast North America. Edmonton: Lone Pine Publishing, 1999