BEGINNER'S ORIENTATION

Identification of plants and animals in biology is frequently aided by using a dichotomous key, a device constructed from a series of highly organized couplets. A couplet consists of (usually) two descriptions which should represent mutually exclusive choices (often it is a particular combination of characteristics that determines the difference). In our keys, couplets are separated from each other by this line:
"~~~~~~~~~~~~~~~~~~~~~".
An OR within a description separates two different characteristic descriptions—one or the other could apply. In rare instances, couplets have more than two choices.

The choices are read and compared with the specimen to be identified. The term specimen is meant to indicate the item under examination, although it is better, if possible, to have more than one individual of the species or item being observed. Once a decision is made at the couplet, the selection directs the user of the key to another couplet (either the next in order or one further on; in our key simply click on the number associated on the right with the selected choice and the page moves to the correct couplet). This step-by-step process is repeated until a conclusion (successful identification) is reached. At this point a verification step is important: compare the specimen with any details in the description and/or any available figures. Also consider habitat and location where the specimen was collected. If the description seems satisfactory, a correct identification probably has been achieved. If the description is not satisfactory in one or more important particulars, back up (the keys are constructed to accommodate this; click on the "origin number" in the second column of the first line of the couplet) to some earlier couplet and start over, questioning each decision more carefully. Be certain you understand the terminology in use in each couplet.

A helpful discussion on using, and making, dichotomous keys may be found in the article A Few Words About KEYS by Gordon Ramel, adapted from Harold Oldroyd (1958). An entertaining discussion on the "what and why" of identification keys can be found at Back Yard Nature.

Here is an example of a couplet in a dichotomous key (this is the first couplet in Keys to Aquatic Biota of the Hawaiian Islands):

	~~~~~	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	1a		Specimen is obviously an animal: showing movement and reactions characteristic of animals, or is easily recognized as an animal (for example, the two nene in photograph above right)	[10]
	1b		Specimen is not an animal; OR does not appear to be capable of movement (swimming, walking, crawling); OR is not readily recognized as an animal (although it may be; like a sponge or a coral)	[2]
	~~~~~	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Note that the description under "1b" could fit some animals like sponges or corals, which do not appear to be capable of movement. This fact will be taken into consideration in the key, and the choice here will not lead directly to plants only. Proceeding further (to the next couplet in the key) is accomplished by clicking on the number link in brackets to the right of the description that best suits the specimen being identified. A blue triangle indicates a link that leaves the displayed page.

It is not unusual to reach a wrong conclusion when using a dichotomous key. Choices must be made all along the way that are not always as clear cut as we would hope them to be. Problems of this sort reflect both the skill and experience of the author of the key AND variability that is inherent in every species population. Also coming into play are subtleties that arise when one attempts to differentiate between two species using just a few characteristics (try yourself to differentiate between cats and dogs using just a few sentences). In some cases, you may find that neither choice fits very well, or you may not always understand exactly what is being asked. It is helpful to write down couplet numbers where there is uncertainty and return to these questionable decisions if the end result is not satisfactory. Because mistakes in interpretation along the way are common, it is important not to accept the answer the key leads you to without then comparing the specimen carefully with final descriptions and/or pictures. Utilize the indentification reached to search the web for pictures and/or a more detailed description. There is no easy way to weigh the importance of each decision made at a couplet, and once a mistake is made, proceeding on to a wrong answer can be surprisingly easy (and obvious only if the verification step is followed). An additional problem occurs when the species you have is not even in the key. In this case, it is very likely not to fit either of the choices at some point in the process because the couplets were developed with specific organisms in mind. Note that you can go backwards in the key by clicking on the number in parentheses at the start of the first description in each couplet, but be careful where a couplet serves as the destination for more than one preceding couplet.

We have tried to mix standard English terminology with specialized terms (the latter often presented initially in parentheses). Any word that appears in bold is defined to some extent at that point in the key and is thus made to stand out in case you encounter the term elsewhere and want to clarify its meaning. Although the keys now have minimal figures, the use of drawings in particular to clarify choices is considered highly desirable, and drawings will be added as the keys are improved over time. Photographs of the organisms treated in the key are being added as these are acquired. In some cases, sources of pictures on the WWW will be listed in our CPIE Hawai`i Aquatic Biota Listing

A different approach to identifying objects (a key can be made for any class of items) is a polychotomous key, also called a "multi-access key". Rather than make decisions on characteristics one couplet at a time, a multi-access key requires the user to select applicable characteristics from a list, submit the selections, and obtain in return a list of possible species that match those characters. This approach can be easier than using a dichotomous key, in particular because it avoids the "roadblock" encountered when neither choice in a couplet can be decided for whatever reason. We have now developed multi-access keys for grasses, sedges, vines, conifers, and trees in the Family Myrtaceae (covering among others, euycalypts) in Hawai‘i (see Multi-Access Key to Plants of the Hawaiian Islands). The CPIE MAK keys to grasses and sedges are integrated with the Keys to the Grasses and Sedges of the Hawaiian Islands, providing links to the final couplets of species in the obtained list. This enables the user to undertake a process of elimination if a list has more than one species, or confirm an identification using photos and descriptions. Aquatic grasses, sedges, and rushes are marked with a dagger (†), if interest is limited to just those members of the group.

This is Page ii [ go back to