What does it mean when a plant name is described as a synonym? And is a synonym “valid?”
It can get confusing when plant taxonomists decide to change the names of plants. According to the International Code of Nomenclature (Melbourne Code, 2011), a replacement name “is a new name based on a legitimate or illegitimate, previously published name, which is its replaced synonym. The replaced synonym, when legitimate, does not provide the final epithet, name, or stem of the replacement name.” To me, that sounds like the synonym is the name which is no longer current. This link from Stephen Saupe of the biology department at St. John’s University, Collegeville, MN is a little easier to understand. Here is an excerpt:
“The correct name for a plant is the oldest, validly published name. Although this sounds simple, in practice it can be challenging to sort through all of the names that have been published for a species and determine which is the correct one.
“Although it may seem that botanists change scientific names just to frustrate us, this is not the case. Names are changed because additional scientific study shows that the original name: (1) didn’t follow the rules (i.e., wasn’t the earliest, or is taxonomic or nomenclatural synonym) or (2) because our taxonomic ideas of the genus and species has changed since the original study (i.e., additional studies showed that two closely related species are actually one). Perhaps this is a good time to mention taxonomists who are ‘splitters’ (focus on the differences between taxa) and those who are ‘lumpers’ (focus on the similarities).”
As you may have noticed, people often continue to refer to plants by invalidated names. And sometimes the rejected names are made valid again later. Unless you are publishing a scholarly article and need to be precise and up-to-date about the plant names, aim to use names that people will recognize and understand.