Name Changes

Plant names are changed for three basic reasons.

1. Nomenclatural (to conform with the rules of the Botanical Code)
A change results in a new correct name while the former name becomes known as a 'synonym' and should no longer be used.

2. Taxonomic (as a result of a revised view of plant relationships)
"Taxonomy is the study of the principles and procedures of classification. A plant taxonomist reconsidering the classification of a particular group of plants has certain aims: to clearly delimit the taxa; to discern natural relationships; to produce a practical classification; and to ensure that plant names are correctly applied in relation to the type specimens." (Oh, so this is what Berg's been doing! :))

3. to correct a misidentification or misapplied name
"Plant identification is the act of determining the name of a plant (botanists actually refer to the is formal process as 'determination').
Misidentification-the act of giving an incorrect name to a plant.
Misapplication- the perpetuation of names resulting from an original misidentification. The name did not change, but the application of the name has.

From source of previous post. :)