Whether you are just starting to explore the local flora or are a seasoned expert, some of you may wonder why scientific plant names change. The short answer is “it’s complicated”. The longer answer is also “it’s complicated”. There will be a number of digressions and side notes in the text below. Skim forward now if you find these tedious.
Before we ask why names change, we should review the basic structure of a plant name. There are common (or vernacular) names and scientific names. Common names are easy to remember but are shunned by the scientific community because the same common name may be applied to:
- Many species in the same genus. In Illinois, Yellow Wood Sorrel is used for Oxalis dillenii and Oxalis stricta.
- Several species in different genera or families. Most bittersweet are members of the genus Celastrus, but false bittersweet is a Solanum.
- A totally different genus! The common garden geranium belongs to the genus Pelargonium and bacopa is a member of the genus Sutera.
The scientific name is, theoretically, more precise, and (no pun intended) specific. We can thank Linnaeus (Carl von Linné) for the two-word form we currently use, composed of a genus name and a specific epithet, followed by the author. The name is not complete without the authority. Why? People disagree. If you wander through technical publications or the internet you may come across the same plant scientific name with different associated authorities! Usually this is because the authors disagree on what group of plants the name in question actually applies to. You might also see auct. non. (short for auctorum nonnullorum, which means “of some authors”) or sensu (meaning “in the sense of”). These are used to indicate the incorrect usage of a name, usually one that has been misapplied. For instance, let’s look at the plant Potemogeton illinoensis Morong. Potamogeton lucens auct. non Linnaeus is a synonym, but only when you see Potamogeton lucens WITHOUT the name Linnaeus associated. Confusing isn’t it? Thankfully plant names are type-based. Each scientific name is tied to a museum specimen (in rare cases an illustration or photo) in an herbarium. When in doubt, you can look at the type specimen and know what the author was talking about!
Why are the scientific names in Latin? Before Linnaeus, the scientific name was a string of descriptors, in Latin. Yes, Latin (albeit with some Greek and other bits thrown in)! The explanation given to me as a student was two-fold. In the mid-1700s, Latin was a common second language for scholars around the world. For this reason, most international correspondence was conducted in Latin. The second important point is that people haven’t been routinely speaking Latin for over 500 years, thus the language is relatively stable. If you want to describe something and not have the meaning change from region to region, and over time, Latin was a great solution. The image to the right is of a letter from Linneaus to baron von Jacquin. In it he describes a plant that was called Theobroma augusta.
To understand why names change (other than disagreements about what a species is or isn’t) you need to consider the stakeholders. Why do we need scientific names and who uses them? Scholarly communication is the reason for the Latin language base, but as noted above, museum specimens exist and need to be stored. If you only need to organize, store, and retrieve specimens (or information) the names can be static. This generally works for museum technicians, field biologists, and many other “users” of plant names. But the inclusion of a genus in the name indicates structure, hierarchy. Hierarchy allows classification, and if you are interested in understanding evolutionary processes, having organisms grouped by their inferred evolutionary relationships, through nomenclature and physical storage, makes learning much easier. So you would probably want all the fern specimens grouped together in the taxonomic key, and in the herbarium!
Continuing with the ferns as an example, in the mid- 1980s the family Polypodiaceae had twenty genera in the local flora. Today there are only two. Most of those genera were moved into different/new families. So the classification of ferns has changed a lot in the last 30-40 years. Some of the changes were triggered by better understanding of fundamental biology (chromosome counts, spore structure, etc.) and some is due to personal preference (shocking, I know). The decision to split up a group or change the rank at which something is recognized can sometimes be arbitrary, but this is rarely the cause of the name changes you have come to despise.
The biggest contribution to the rapid rise in changing plant names is due to a wealth of new (often molecular) information and better computation tools (software and hardware). Better and more data, plus better tools allow us to make better inferences, especially among species in difficult groups. Let’s take a look at goldenrods. The genus Solidago includes the bulk of the species (still), but several [S. graminifolia (L.) Salisb., S. gymnospermoides (Greene) Fern., and S. tenuifolia Pursh] are now included in the genus Euthamia because a variety of data (DNA, morphology, etc.) show that they are not actually very closely related to Solidago! Oligoneuron species however are just specialized Solidagos! The University of Waterloo has a short discussion that you can reach via this link.
Names change to better reflect our inference of the evolutionary history of the plants. Keeping them in the wrong genus (or family, or order) would be positively misleading. Thankfully specific epithets generally don’t change, and if they do, it is because the name is already in use for another species. If you want to read more on the rules for naming plants, check out the most recent International Code of Botanical Nomenclature here.