Best Practices

A variety of tips and tricks for using Lucid keys

This section is adapted from Lucid Player help ( and USDA-CPHST Lucid training workshops.

During an identification session, Lucid allows you to choose any character (i.e., a feature and its associated states) from the Features Available list at any time. However, “stepping” through the key in a structured and sensible way will make your task of identification more efficient. Below are recommendations for increasing your efficiency and decreasing the amount of time required for identifying an unknown specimen using Lucid Player.

Become familiar with the specimen

First, become familiar with the characteristics of the specimen you wish to identify. If you are also familiar with the keys in this tool, then you may already know many of the specimen's characteristics. Briefly reviewing these characteristics before you start will make it easier for you to proceed through the identification.

Note and use distinctive features

Some taxa may possess particularly distinctive features and/or states. Use of these may allow the taxon to be keyed out in just a few steps. At the very least, starting with any particularly distinctive or striking features your specimen may possess may quickly reduce the list of Entities Remaining.

Answer easy features first

Browse the list of Features Available and address easy features first. The principles of dichotomous keys, in which the couplets must be answered in a preset order, are very familiar to most key users who often automatically apply these principles to a matrix key. Although Lucid lists the features of a key in an initial sequence in the opening window, this does not mean that the features must be selected in that order. You can select any feature from any position in the list. [Note that in some keys, where positive dependencies are used, you may be forced to answer specific questions before others become available.]

Most Lucid keys will have a wide variety of features, ranging from those dealing with obvious and simple features to those dealing with features that may be minute or difficult to interpret. Always start by browsing the list of Features Available for obvious features that you can quickly answer, as opposed to getting stuck on the first one. Lucid software is designed to overcome problems associated with difficult features.

It's okay to skip features

In looking through the features, you may not be sure which state of a feature to choose, or a feature or state may not be clear on your specimen. Skipping the feature entirely in such cases is always an option.

Use illustrated feature notes

As you work through the list of Features Available, you may find some features or feature states that you do not understand. If so, review any explanatory notes and/or illustrations that may be associated with the features and states. In fact, it is a good idea to check the notes and illustrations before using any feature for the first time, and to become familiar with these for all the features.

Choosing multiple states

You can always choose multiple states (more than one state of a feature) if you are uncertain which state is the correct one to choose for a particular specimen. Lucid software is designed to allow you to choose as many states as you require from any one feature (if, for example, your specimen is in between two states, or exhibits two or more states). Within the program's logic, these states will be connected by an “or” link. This will cause Lucid to search for all taxa with any of the states you select. As a general rule, if you are unsure which of two or more states your specimen has, then choose them all. That way, you can be sure that your target taxon will remain in Entities Remaining. [Note that in the Lucid3 Player users can choose the matching method option of “all states” rather than the usual default of “any states”. See Help for more information.]

Finding the best feature to address next

When you have dealt with all the obvious features, use Lucid's “Best” function (the "magic wand" icon) to suggest the remaining feature that will give you the most efficient next step. The Best algorithm will assess which of the remaining features and states available will best reduce the list of Entities Remaining. The Lucid Player has two “Best” modes: Find Best and Sort Best.

    Find Best – In the Lucid3 Player, clicking the Best button will cause the Player to move to and open the best available feature. Next Best and Previous Best buttons on the toolbar allow navigation through the Features list, if you have difficulty addressing the first feature nominated. If the list of entities in Entities Remaining changes after choosing a feature as suggested by Best, you should click the Best button again to recalculate the best feature to address next.

    Sort BestSort Best will reorder the Features Available list so that features are sorted from best to worst. After a Sort Best, scan the top of the list for features that you can answer most easily. [Note that Sort Best only works using List View, as a tree representation of features cannot be sorted.]

Other Lucid3 Player tools

You may find other Lucid3 tools helpful while navigating feature choices, such as Shortcut Features, Prune Redundants, and Calculate Differences. Explanations about how to use these functions are available through the Lucid Player Help menu.

What if no taxa remain?

This will happen sooner or later in one of your Lucid sessions. If no taxa are listed in the Entities Remaining window, then it simply means that no taxa in the database match the set of states you have selected. Several explanations are possible, but these are some of the most common:

  • You have made an error in one or more of states you have selected. This is the most likely error for any situation in which no taxa remain.
  • The taxon may be undescribed or not included in the key. In this case Lucid cannot identify the specimen because its features are not represented in the key's data tables.
  • The key author may have made an error when constructing the key. This is unlikely, but it can happen. If, after carefully checking all the features and states and checking that the specimen you are attempting to identify would be expected to be included in the key, then a key construction error may be present.

Whichever of the above situations is suspected, you must very carefully review your chosen features and determine which ones you are uncertain about. Try unselecting uncertain states one by one to see what effect each has. One or more taxa may move back into the Entities Remaining window. In difficult cases, you may need to “play” with the key, adding or deleting states progressively to try to find the best matching taxon.

What if several taxa remain?

Never assume that you will always end up with one taxon remaining. Some taxa in the key may be very hard to differentiate, except when using difficult or obscure features. Sometimes, after you have addressed all the features, you may have a short list of taxa remaining instead of just one taxon. You are still much closer to an identification than you otherwise would have been. You may then have to carefully check your specimen against associated information (descriptions, images, etc. for the remaining taxa) or refer to more advanced or specialist reference sources.

In some cases, if you have a short list of taxa remaining, but have not addressed all the features, it may be easier to check your specimen against information associated with these remaining taxa. This can sometimes be faster than trying to find a feature that will discriminate among the remaining taxa. If your taxon does not look similar to any of the taxa remaining, you can use the same strategy described above, of unselecting states one by one, or “playing” with the key, to find the best matching taxon.

Checking the result

Once you have made a preliminary identification, check the other information (descriptions from the fact sheet or the image gallery) provided for the taxon. Getting a possible name for a taxon from a key is not the end of an identification. You may have made errors, or your specimen may be a taxon that is not in the key. In these cases, the key may have provided you with the wrong name. The associated information will often give you a good indication as to whether the answer is correct.