CPIE Project

Page ii


    BEGINNER'S ORIENTATION Nene - Hawaiian goose

    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 represent mutually exclusive choices (often it is a particular combination of characteristics that determines the difference). Be aware that in a few rare cases, couplets actually present three choices (a, b, and c). In our keys, couplets are separated from each other by a line like this:


    The two (or three) choices are read and compared with the specimen needing to be identified. The term specimen is used to indicate the item being examined, although it is best, 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 to another couplet, either the next in order or one further on. In our key you should note this next number, then simply click on it (number is in brackets on the right of the selected choice) and the page moves to the correct next couplet. This step-by-step process is repeated until a conclusion (successful identification) is reached. At this point a verification step is very important: compare the specimen with any details in the description and/or any available figures or photos. Also consider habitat and location where the specimen was collected. If the description seems satisfactory, a correct identification probably has been made. If the description is not satisfactory in one or more particulars, back up (the keys are constructed to accommodate this; click on the "origin number" in parantheses in the second column of the first line of a couplet) to some earlier couplet and start over, questioning each decision more carefully. Be certain you understand the terminology used 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). A detailed discussion on the "what and why" of identification keys can be found at Back Yard Nature.

    Following is an example of a couplet in a dichotomous key (this is the first couplet in Keys to Aquatic Biota of the Hawaiian Islands; if you are here from Keys to the Grasses of Hawai‘i, that first couplet is found on page iii):

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 well be) [2]

    Note that the description under "1b" could fit some animals like sponges, 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. Indeed, we are considering expanding the keys to include certain physical (geological) features and specimens to enhance an ecological approach to aquatic biology. Choice "1b" fits as well for a rock. Advancing to the next couplet in the key is accomplished by clicking on the number following the description that suits the specimen being identified.

    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 discussed. 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 and/or bold text). 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. Perhaps a glossary can be added some day. 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

    This is Page ii [go back to page i] | [go on to page iii] | [Return to page i of Key to Grasses]

© 2011, 2012, 2013 AECOS, Inc. [FILE: keys_intro2.html] 1