What is an identification key?

Introduction to identification keys

If you want to identify a tree, a weed, a bird, or an insect, how would you go about it? To identify a bird, you might use a published bird book or a bird app – and flick through the images. You might do the same for certain tree species.

However, if you are in Australia and you want to identify a Eucalyptus tree, there are over 1,000 Eucalyptus species, and even more species of Wattle. Scanning through a guide-book of tree images to make an identification is likely to be tedious; using a book of images  to identify an insect species is likely to be far more challenging. Since the 18th Century, scientists have worked on what they call identification keys to provide a more systematic way of helping people identify insects or plants.

So what do we mean by a key? Most people will think of a key as a means of opening a door into a house or a room, or possibly a key to open up a locked filing cabinet, enabling you to access information that has been filed within that cabinet. In this sense, an identification key performs a similar function to a key to a cabinet. Therefore, if you use a Lucid key to identify a plant or an insect (i.e. by its scientific name), it will be like opening up a filing cabinet, enabling you to access information about that particular species, including its biology, life cycle, the value or danger it presents, and so on.

As a special form of an “expert system”, Lucid keys, developed by taxonomists, agronomists, health, or other experts, enable users to tap into this expertise to help identify animals and plants, diagnose crop or health problems, select plant species for specific situations, or provide “expert” support for other problems

Dichotomous or pathway keys

It was during the time of Linnaeus (1707 – 1778) that naturalists and taxonomists first developed and published identification tools as dichotomous, or pathway, keys. A typical form of a printed dichotomous key is shown below, showing only the initial part of a key for determining the Order to  which an insect specimen belongs. The pathway taken through the key is determined by the decisions taken by the user at each branch in the key, by comparing the features of the unidentified specimen with the descriptions (and possibly images) described in the two couplets at that point.

 Section of a dichotomous or pathway key to Insect orders

 By choosing that component of a couplet that correctly describes the specimen, the user is led down the path to the next relevant couplet. For instance, in the insect Orders key above, if components 1(a), 2(a) and 3(a) are correct descriptions for that particular specimen, then it is identified as belonging to the Order Diptera.

While dichotomous keys are still published in books and journals, digital technology enables them to be published online, allowing users to follow a pathway of characters (often illustrated) by moving from one web page to the next. However, this can become an onerous process for large pathway keys. The development of Lucid Pathway key software has provided a novel solution to this problem.

Lucid Matrix keys

It was only with the Information and Communication Technology (ICT) revolution, in the 1970s and 80s, that software became available, allowing different, matrix-based, identification tools to be developed.  One of the earliest matrix key programs was the DELTA System, developed during the 1980s at CSIRO in Australia. Two other systems were developed in the 1990s, the Lucid system, initially developed at The University of Queensland, and the Linnaeus identification system, developed at the University of Amsterdam, and now incorporated in Linnaeus NG.  

The process involved in developing a matrix key, is shown in the diagram below, which also is a key to insect Orders. To set up the Lucid matrix, information is required for the two axes involved: a list of the taxa covered and a list of those morphological features that are important for making an identification. The cells in the matrix, each  representing a feature/state associated with a specific insect order, are scored for presence/absence, common/ rare, misinterpretation (where users are likely to select a feature/state by mistake), etc.

Lucid key components

Lucid key components

Once the data has been incorporated and scored in the key builder, images and supporting text can then be linked to the key’s feature/states and taxa to provide help in making an identification. When a key is completed, it can be deployed online, as a mobile app, or on a HDD/USB/CD/DVD. The figures below shows the Insect Order key displayed in two different player formats:

The 4-window format for an internet or desk-top player, showing Features – available/selected; Taxa – remaining/discarded; 

The single screen format for smartphones and tablets. In this case, the “Features” screen allows users to select relevant features/states exhibited by the specimen but, at any time, the “Remaining” entities screen can be accessed by swiping left or via the options shown at the bottom of the mobile screen.

Examples of Lucid keys

While Lucid keys can be deployed as CD/DVD and USB products, many Lucid keys are now deployed via the web. Examples of Lucid keys developed for a range of purposes, including plant and animal identification, crop and human health diagnosis, and plant selection, can be accessed by returning to the Lucid Keys introduction.   

Lucid Mobile apps

To increase the range of situations where Lucid keys are likely to be used, such as field work in situations where mobile connection is unavailable, the Lucid team have developed a generic Lucid Mobile platform. This means that any Lucid key, developed using a recent version of the Builder, can be published as a Lucid Mobile app. Many of these apps are free to download from Google Store (Android) or iTunes (Apple).