Using Dichotomous Keys

Apart from the initial shape key, the other keys follow a dichotomous style. If you've never used a dichotomous key, approach it as you would a roadmap in the sense that a map and a key are devices to help guide you to a desired destination. With fungi, the correct destination is the identity of the species in hand. Just as following directions while using a map involves decisions to use one road or another (forks in the road), dichotomous keys are also a series of decision points (dichotomies) where the user must decide which of two directions best matches the specimen at hand. In the key, each decision point is called a couplet and each alternative decision is called a lead. If the user makes the correct decision at each couplet, the destination (i.e., correct identity) will be reached.

This imaginary key to seven people illustrates how dichotomous keys work:

1.  Person female
     2.  Hair brown
          3.  Eyes blue .............................................................Person A
          3.  Eyes brown ..........................................................Person B
     2.  Hair blonde
          4.   Person taller than 5 feet, six inches ........................Person C
          4.   Person shorter than 5 feet, six inches .....................Person D
1.  Person male
     5.  Eyes brown ...............................................................Person E
     5.  Eyes green
          6.  Person weighs more than 200 pounds ...................Person F
          6.  Person weighs less than 200 pound s......................Person G

Given this key and a 175 pound, green-eyed male, the person would be identified as person G.

Note that the two leads of a given couplet do not necessarily occupy two sequential lines. The two leads of a given couplet will have the same number or letter and will have the same indentation from the margin. Because of the large number of species of poroid and gilled fungi, the keys to these groups are first divided by an initial key into several smaller keys.

Eventually, the key will lead you to a species name. Scientific names are used exclusively in the keys and species lists. This usage reflects the actual practice in mycological circles, whether amateur or professional. Common names of some fungi exist but they are not standardized. For clarity of communication, it is best to become familiar with the scientific names. The scientific name in the key links to a page where the species is further described and illustrated.

Keep in mind that things can go wrong when using a key. Some errors are user-caused such as not taking the time to understand the terms, not reading both leads, or choosing to work with a rotting specimen. Others are the fault of the key including mistakes, ambiguous leads, or not taking into account the variation possible within a species. Specimens that are too old or too young will usually not work. It is quite possible that the key simply does not include the specimen you found. Despite the potential shortcomings of keys, they remain useful devices for identifying organisms such as fungi. Keys require the user to make careful observations of the specimen at hand and to learn the essential vocabulary needed to describe macroscopic fungi. Good observational skills and familiarity with mycological terminology become even more critical when dealing with the many fungi which cannot be reliably identified solely on macroscopic characters.

It is said that keys are written by people who do not need them for people who cannot use them. I'm more optimistic. Although the keys are written with the novice user in mind, the user must become familiar with the terminology used in the key. Consult the glossary as needed.