When trying to determine the identity of an unknown plant one method of identification involves reading written descriptions of a group of possible plants. This first requires that the plant of interest can be narrowed down to a few species. An informal way of doing this is to examine descriptions in floras or field manuals (published descriptions of the plants of a particular region, geological period, or environment); formal monographs (publications on specific groups of related plants) can also help narrow your search. Otherwise, the identifier would have to read every possible description of plants in the world!
Written descriptions can be long comprehensive descriptions detailing all the characteristics of a plant species and can include value ranges for several characters. These types of descriptions are required when new species are described. This can help the description user to examine the plant carefully and fully determine if all the characteristics match the detailed description. One of the drawbacks to these long written descriptions is they do not really tell you the key diagnostic characteristics of your specimen. Sometimes there is just too much information to be helpful.