Edibility by the numbers

I’ve been interested in doing some work with mushroom data for quite a while now, and only over the past year or so have I managed to discover tools that would let me do what I want. I thought it might make a nice pilot project to do some statistics on mushroom edibility, since I get asked about this – how many mushrooms are poisonous? and how many are edible? – surprisingly often.

When I put up the original Mushroom the Journal website, I devised a system of automatically cross-linking author and mushroom names that were mentioned in articles, so I have 2037 species of fungi in the database that I used to generate those pages. I figured I’d work my way through them, add edibility ratings to the fungi in the database, and see what the numbers say.

Kinds of Edibility

Mushroom edibility has some rather strange problems of terminology, abetted by the untrustworthiness and cover-your-behnd-ness of many field guides. For instance, many field guides use the term “inedible” for “I don’t want you to eat this, but I don’t have the slightest good reason for that.” They will also sometimes use the phrase “not recommended,” which you’ll notice is not an actual kind of edibility. In my treatment, I reserve the term “inedible” for things that have a textural reason for not being edible: various polypores that are to hard or tough to eat, for example.

On the poisonous side of things, I distinguished between mushrooms that are “slightly poisonous” (will make you throw up, sometimes for quite a while), “seriously poisonous” (potentially life-threatening) and “deadly.”

There are also quite a few situations where we really don’t know the edibility of a mushroom, but we presume that it’s poisonous because it’s closely related to a poisonous one. For example, some Lepidellas like Amanita smithiana and Amanita thiersii have emerged over the past decade as being seriously poisonous; so we presume that at least some of the other Lepidellas out there are poisonous in a similar way.

Likewise, there are some Clitocybes that are “known” to cause stomach upset, and there are others that look very similar but haven’t been specifically tagged as being poisonous.1 So these get tagged as “presumed mildly poisonous.”

I actually invented a category “choice non-standard” for things that are very good but haven’t made it into the field guides yet. I also placed the lingzhi polypores in this group, as they’re not choice edibles in the usual field guide sense, but they are highly prized by some people.

“Tough” is another category that might need some explaining. These are mushrooms that are definitely known to be edible, but are also too tough for normal cooking methods – they need to be stewed or baked for a long time. Pleurotus dryinus and non-young Meripilus giganteus fall into this category. Similar is “Edible when young” – Bondarzewia berkeleyii, for example, is eaten by quite a few people when it’s still in the “lumpy fingers emerging from the ground” stage. At that point in its development, it shows its biological identity with Lactarius by giving milk when cut, and having something of the same consistency as them. But when it gets older, it gets very rubbery and develops a disgusting odor.

The category “tastes too bad” I used for mushrooms that are acknowledged as not poisonous but taste too bad for most people to be able to eat them – for instance Russula krombholzii or Amanita citrina. It’s possible that this category could have been combined with “inedible” – and perhaps for some statistical purposes I will – but as far as basic categories are concerned, this seemed to be a clear distinction that may have some value.

So far, I’ve only found the time to assign edibility ratings to 442 mushrooms, but that’s still something of a decent sample size and I thought I’d share my preliminary findings with you.

The Data

Let’s take a look at our selection of mushrooms, graphed in order of edibility.

When pressed for ballpark estimates in the past, I’ve suggested that edibility falls into a crude bell curve, or normal distribution: small numbers at the extremes of edibility or poisonousness, somewhat larger numbers at less extreme values, and a big pile of “everything else” in the middle. This is roughly the distribution that the data show. For instance, if we take everything that’s definitely edible (“tough” and everything to the left of it) and everything that we’re pretty sure is poisonous (“presumed mildly poisonous” and everything to its right) and compare them to the categories in between, we get the following table:

More data: edibility vs poisonousness

So yeah, there’s that big bump in the middle, but another interesting thing is that there are only about 2/3 as many poisonous mushrooms as edible ones. What’s more interesting is where the difference mostly lies. Let’s look at a set of individual match-ups, from the extremes on in:

The big difference in numbers is between the really good mushrooms and the deadly ones. The difference is all the more striking because I’ve been working on these mushrooms starting at the beginning at the alphabet (I’ve gotten about up to the end of the letter C) so this sample includes the Amanitas. We’ll see how this and the number of hallucinogens (watch out for the Ps!) develops as I work my way through the alphabet.

Different Categories of Ignorance

The other striking thing about these statistics is how many fungi are of unknown edibility. I mean, edibility has been a prime motivation for hunting mushrooms for time out of mind, and yet if you look at the largest categories here

you see that the largest three categories are different kinds of ignorance. And they are far larger than the other categories: the three of them average out to a value of 58, far above the first known category with its value of 37.

If we add up the mushrooms in the “known” categories vs the “unknown” ones:

Now, it isn’t a colossal difference, certainly. But I can’t think of another field where – at this stage in history – ignorance is actually in the majority in such a fundamental aspect of why humans are interested in this field.

I want to emphasize that the mushrooms in the categories of “insignificant” (=”too small to bother with”) and “microscopic” really are unknown. They really can go either way. For example, Galerinas were undoubtedly in the “insignificant” category until a NY mushroom-hunter in the 1970s decided that they were honey mushrooms. On the other hand, the micro-fungus Fusarium is a plant parasite, and its effects can be disgusting and bizarre enough to assume that it’s not edible. But the British have cultivated it in vats and eat it under the brand name Quorn – more evidence that anything the Brits consider edible probably is.

Again, it’s interesting to do individual match-ups between analogous pairs of categories:

We don’t have any “presumed good” or “presumed choice” mushrooms because people have tried all of those already. We don’t have any “presumed deadly” ones, sadly, as the deadly category has been populated by personal experience. I may have to add that category when I hit the Gs and rank the Galerinas. But there aren’t going to be very many of them. The presumed poisonous categories are mostly populated by the Lepidellas and Clitocybes mentioned above, plus a surprising diversity of red-pored boletes that North America turns out to have.

Quality of Data

Even in categories where we know whether the mushrooms are edible or not, there’s a problem with the trustworthiness of our reference material – look at the two highest categories of edibility. These are “choice” – which is a generally-agreed-on quality given in all the books – versus “choice non-standard”, which are really good mushrooms that the books waffle on.

For instance, here at the beginning of the alphabet, I’ve put a bunch of red-staining Agaricus species in the “choice non-standard” category. These are really really tasty mushrooms, but the books always hedge their endorsement of them, saying that “some people throw up” or some such nonsense. In fact, some people throw up with any species of Agaricus (except perhaps the Bitorques) but no one feels obliged to give a bunch of disclaimers about the other ones. But somehow, historically, some field guide must have mentioned someone having a problem with the red-stainers and everyone since has copied it.

In my experience, they’re not found very often, so that might have something to do with it – a large and obvious population of people who eat them and don’t get sick might have swayed the official opinion. But there hasn’t been this widespread sampling, and so this official state of confusion has remained.

In any case, if we compare them head-to-head,

we see that the choice non-standard mushrooms are just a hair under ¾ the number of what we might call “officially choice” mushrooms. That’s not a majority of ignorance, certainly; but it’s not a ratio that any scientific field would be proud of.

Conclusions

Well, you know the standard scientific conclusion for mycology: “More work is needed!” I now have edibilities assigned for almost half the species in my database, but I’m also more wrapped up at the moment in other data endeavors, and also the editing of articles for the next issue of the magazine. I’ll give the edibility stats another shot once I get the next issue out in January. In any case, I hope this will be the beginning of a fruitful re-examination of our knowledge of mushroom edibility.