Instructions for Keying Plants


 Traditional dichotomous keys used for identifying vascular plants, especially those designed to identify plants of large geographic areas, such as countries, states, regions, or continents generally follow a hierarchical multi-step prescribed processes, forcing the user to select morphological characters in a predetermined order to achieve identification of an unknown plant. The hierarchy generally begins with a family key and is then followed by generic and specific keys. The obvious weakness of this type of key is that if the specimen lacks a particular morphological character necessary for keying, the keying process terminates at that point. Conversely, the advantage of this type of key is that the key developer can be far more precise in forcing the user to follow specific steps to help guide the user through the process, thus reducing the risk of misinterpretations and misuse of characters.

Random access keys differ from dichotomous keys by allowing the user to select randomly, any character or set of characters (character states) in the order of convenience or ease of use. The advantage of this system over traditional dichotomous keys is that very obvious, easily observable structures or characters can be applied first, i.e., plant habit or habitat, flower color, armament, leaf position or type, fruit texture, etc., few if any of which are used as lead characters in traditional, dichotomous keys for large geographic areas.

Like dichotomous keys, random access keys also have disadvantages, the most serious of which is the quantity of time necessary for the developer of the key to populate accurately all characters shared by a particular plant and to establish the precision necessary to direct the user to interpret those characters accurately every time they are used. For large floras, many months can be spent populating all species that share a single character, i.e., flower color or flowering time. Moreover, since the degree of morphological variability can be enormous, when used early in the key, such characters can cause system failures.

With a thirty-year history in developing random access keys for various federal governmental agencies, we’ve discovered that mixing the concept of hierarchical family keys with the random access process, and then incorporating phytogeography and photographs, offers the best results and the highest degree of accuracy in keying.


Here is how the BONAP plant keying process works:

STEP 1 – Select your county or zip code by using the “Search by U.S. Zip Code, County or Location” located below the buckskin-colored “State-Level Query Map.” Alternatively, you can select your state or geographic area from the Query map.

STEP 2 – Scroll to the Family Identification Key. Proceeding from left to right, select character states that match your plant. Open each character box found within the five columns. The various columns reflect characteristics for each major plant organ and are preceded by a column of general characteristics. Character states shown within the pale blue color are deemed to be most effective in reducing possibilities, most easily observed and most universally understood by users in keying.

NOTE – Do NOT guess. It is unnecessary to attempt to score all characters and character boxes. Score only the ones for which you feel certain.

Once you have completed scoring the family key, click the green-colored “Run Query” button below the key. You will notice that the three nomenclature columns (on the right side of the page) contain the names of the plants that remain. Remember: This is a family key, designed to key plant families globally, which I have modified to include North American plant families only. Therefore, it may seem odd to North American users that certain families still remain after certain characters have been selected.

Also, remember, this is a family key only. Therefore, the genera and species remaining may or may not necessarily reflect the characters you selected for the family keying process. Many of these genera will be eliminated by the selections made in the next step (Step 3: Biological Attributes Portion) of the keying process.

STEP 3 – Proceed by scrolling to the Biological Attributes Query box. For your convenience, we have arranged the attributes sequentially, by order of ease of use and significance. Click on every category and subcategory and select all of the characters that best reflect the condition of your unknown plant. Unlike the Family Key, it is important to score as many of the attributes as possible, but remember not to guess.

IMPORTANT NOTE: Even though you may have scored a character in the Family Key, it is essential that you score it again in the Biological Attributes Query, since you are now attempting to key species or small group of species. Once you feel that you have entered all character selections, click the Run Query button to determine the species remaining. If numerous plants still remain, you can return to either the Family Key or Biological Attributes Query to determine if additional characters might reduce further the remaining plants. Once the keying process is completed, you can engage the Image Gallery to match the unknown plant with the available photographs. Remember that the keys are designed for flowering plants only. Keys for grass-like plants are under development.

IMPORTANT NOTE: While keying, one trick to help reduce errors and confusion is to engage “Run Query” after each selection in both the Family Key and Biological Attributes, thereby reducing the possible character choices remaining via eliminating (graying out) characters that are no longer applicable.

***Although we had considered incorporating additional Boolean logic of “OR”, “NOT” and “AND” into these keys, such additions (e.g. “OR”) can often weaken the effectiveness of a key by including more plants that share certain characters. Also, since the use of “NOT” is often misunderstood and causes unintended elimination of species, we have decided not to include it here.