Dichotomous Keys

The Principle of Priority:

In order to have a definite starting point, botanists have agreed that for flowering plants the starting point shall be Linnaeus' Species Plantarum, published in 1753.

The International Code of Botanical Nomenclature lists exceptions and additions to this rule. This code is supposed to keep botanists all over the world using the same system of names. However, there is disagreement over some plant groupings and today we have several proposed classification systems. Some of these systems have 20 or more principal groups of plants. Complicating matters farther, the major classification groups for botany and for zoology are different. There is a movement to adopt only one classification system, the BioCode for all types of living things.

To avoid confusion, most literature usually refers only to family names and the genus and species of individual plants.

The "Type" Method:

Holotype (Type Specimen): The original specimen designated by the author. "Types" are the most valuable of all specimens.

Isotype: Any specimen, other than the Holotype, that duplicates the Holotype. The isotype must come from the same collection, with the same locality, date, and number as the Holotype.

Lectotype: A specimen selected by a competent person from the original material studied by the author.

Neotype: A specimen selected to serve as a substitute for the Holotype when all material on which the name was based is missing.

Botanists have adopted the following method to stabilize the determining characteristics of a species:

The author of a species must designate a certain specimen as the Type Specimen of that species.
The Type Specimen is not necessarily the most representative of the group, it merely best shows the element on which the name for the group was originally based.
The Type Specimen fixes the strict concept of that species and the application of its name.
The Type Specimen is carefully preserved in a herbarium accessible to research scientists.
To allow for damage or destruction of the Type Specimen, the system of Isotype, Lectotype, Neotype, and others was devised for designating acceptable substitutes.

Universities and museums are very proud of the number of "Type Specimens" they have in their herbarium.