Any time I want to see what a fictional mushroom could correspond to, I go to MycoKey.
I first learned of MycoKey when I was working at the New York Botanic Garden. Roy Halling, the NYBG’s Curator of Mycology, showed me the software and was kind enough to give me one of his licenses so I could work on identification on my own. The software was developed by two Danish researchers, Jens H. Petersen and Thomas Læssøe. It is currently in beta (version 4.0 and trademarked, but still technically in development).
Using the Key
The intuitive key lets a mycologist click through illustrations and select specific colors, making it much more beginner-friendly than a traditional paper key.
A Note on MycoKey Color Selection
The software has an incredible palette of colors to choose from. This takes a lot of the guesswork out of color identification, and it is one of the things that endeared me to the program early on. There is something called “Mycologist Pink” that threw me off on a couple of my early collections. Identification keys will describe spore prints as “pink”. In my mind, that means, well, pink – what the MycoKey color selector might call “Clay Pink to Rose.”
But it turns out that when mycologists say “pink”, they are talking about something more along the lines of “Buff to Pale Brownish”. I got rid of my (brown) spore print because I thought I had messed it up somehow. It was a beautiful, full, round print, and I got rid of it because I thought it wasn’t going to be useful for identification. I think about that a lot… And it’s an issue that MycoKey could have prevented.
It isn’t foolproof, of course: Many mushroom species have variations that the key can’t account for, and while the color selector is great to have, the difference between “yellow-brown” and “muddy yellow” may be different for different people. On a paper ID sheet, you can just agree that the color is “Buff to Pale Brownish”. On MycoKey, you have to try to be more specific. This can be awesome, as I’m sure Dr. Petersen and Dr. Læssøe put a lot of time and image searches into determining the specific categories for color.

On the other hand, I’ve also had many specimens that fell somewhere in between MycoKey color categories, and there are a lot of cases where fungal genera have variable colors and descriptors like, ‘Cap can be yellow-green to vivid brown’. Which color category should I pick?
On the bright side, though, MycoKey will help me visually identify a shade of “Vivid Brown” that I may have considered red or orange on a written key. On MycoKey, that could bring me to the right genus, whereas in a traditional key I might follow the wrong branch and have to backtrack later.

In fact, it was through MycoKey that I learned the difference between “Vivid Brown” and “Dull Brown”, which has helped me on written keys I encountered later.
Moving Through the Key
I like MycoKey’s illustrations a lot, especially for folks just starting out. You may not remember offhand the difference between adnexed and adnate lamellae (gills), especially if you haven’t keyed out a gilled mushroom for a while. But MycoKey’s illustrated cross-sections have you covered.

I also appreciate the combination of illustrations and descriptions, so that if I have, say, a pileus that looks unfamiliar, using MycoKey will give me the words I need to identify similar caps later.

It’s also fun to watch the sample mushroom change as you enter more information. The cap changes shape and texture, the colors shift, and while all this is happening you also get a live listing of species that match the descriptions you’ve put in – with indicators of how closely they match your data!
Once you’ve narrowed down your list, you can look at photos and genus descriptions from the MycoKey database to see how they match your specimen. Species are available for some genera, but not all species are available with this key. If the genus description seems to match your specimen, but you can’t get down to species with MycoKey, at least you have a much narrower search ahead of you!
Other Caveats
The website currently only lets users look for cap-and-stem mushrooms (so no stinkhorns, coral fungi, or brackets). However, that does give you over 2600 species of agaric and bolete mushrooms (basidiomycetes), with more than 8500 pictures.
You can get access to the stinkhorns and others by buying the full desktop version. There is a 14-day free trial of the full version, but unless you are hoping to blitz through a whole lot of specimens after a very lucky hunt, I don’t know how far that will get you. The full version is US$55, so if you are just starting out, maybe you can go splitsies with a friend?
Conclusion
I love MycoKey. The tools are intuitive and I frankly think it’s fun (and enlightening!) to play around with. Whenever I see a mushroom in a video game and wonder, “Could that be based on something real?” I go to MycoKey first. If paper identification trees are frustrating me, I go to MycoKey. And if I’m being truthful, if I forget how to describe the lamellae on a new specimen… yeah. I head to MycoKey.
And while I’m being honest, yes, I do like to see how crazy my color combinations can get and still match real mushroom descriptions.

Hee hee.
And, of course: Don’t eat something just because MycoKey says it’s edible.
Check with an expert. Always.