How many mushrooms are there?
For most of us, wild mushrooms are exotic creatures. We have spotted them in the supermarket now and then, but they do not populate our childhood books the way cows and lions do; we do not learn to distinguish their infinite varieties in the course of everyday life, the way we do with dogs or cars. They are the sort of organism that we usually learn about from an educational TV program, where the camera shows us exactly what this strange new thing looks like while a calm authoritative voice tells us its name, its favored location, and some other interesting facts. Naturally, we expect a similar experience when we learn about mushrooms: we want to open a book and see a detailed account of every mushroom we might encounter, like we get in a book on birds.
Mushrooms don’t work that way. There are a number of reasons for this. First of all, we have about 11,000 named species of mushrooms in North America. That’s just the macrofungi, the fungi that are large enough to see easily.1 For comparison, we have 200 species of bird in all of North America, and just short of 1000 mammals. The largest field guides for North American mushrooms have almost 2000 species listed. That’s enough for all the birds and mammals in North America with space left over for over 700 insects; but it’s less than a fifth of the known species of mushroom.
The other main problem is that – by various methods of estimation – only 5-10% of our mushrooms are scientifically described and named. This There are two main reasons for this: a lot of mushrooms look alike, and much of the continent just hasn’t been well mycologized. Because mushrooms look alike, there are often several species in different areas of the country going under one name.
Part of the problem is that the mushroom you see is only the fruiting body of the fungus. It’s sort of like trying to tell plants apart just by looking at their fruits: you can certainly make progress, but not being able to look at the leaves or flowers is a big handicap – not to mention that the fruits are only out for a small fraction of the year. Even so, some species are cryptic: they simply can’t be told apart from each other by any means that you can see. Some cryptic species can be distinguished by microscopic features like spore size; but others can only be identified by trying to mate them with cultures of known species, or by DNA sequencing.