What’s So Hard About Naming a Plant?
How hard can it be? You see a plant, you give it a name, you're done. Why does a single plant sometimes have so many names?
Botanists give each plant a scientific name, simply because there is no such thing as a universal common name. "Common" means a name commonly used, but these names vary enormously—some plants have eight or more common names, and many more in other languages. If that isn't enough, different plants sometimes share the same common name. So if two botanists need to make sure they're discussing the same plant, they need a more formal system.
The grand poohbah of taxonomic organization, Swedish botanist Carl Linnaeus, created a naming system designed to do away with the ambiguities of common names. He didn't choose Latin to be ponderous and academic, but simply because Latin was the closest thing at the time to a universal scientific and clerical language. In the 1700s, if you wanted to make yourself understood to other specialists, you wrote in Latin. One of the most useful legacies of his naming system is that it is employed even by speakers of non-Roman languages, so it continues to be a universal system.
Linnaeus' system is called the binomial naming system, because he employed two names for each living thing, a genus and a species. The genus is the name for a group of related plants (or animals); the species is the name for a specific one. He chose names based on observed similarities. But as we began to learn that plants evolve into particular shapes to fit particular ecological niches, we found that similar-appearing plants weren't necessarily related. In one habitat, a lily might evolve into a shape to attract a particular type of bird; in another, an aster. Sometimes new information makes it necessary to change a plant's genus to place it in the correct part of the family tree.
But it gets more subtle. Even identical species can produce different forms in different habitats, perhaps differently colored flowers, or leaves with two lobes rather than three. Are the forms different subspecies? Are they unique species entirely? Did they evolve independently, or from a common source? Or are they different for some environmental reason, like blue hydrangeas, which vary from blue to white based on the amount of aluminum sulfate in the soil?
Then there is natural cross-breeding. Closely-related species often produce natural hybrids, part of the process of evolution. Most such hybrids don't persist for more than a few generations, but they are common enough and varied enough to confound even the most careful observers. When is a natural cross recognized as a unique species? There is no easy answer.
Suppose that two botanists independently report the discovery of two subspecies of a plant. If both subspecies are later found to be normal variations of the original species, the original species now has three names—the original one and the two reported subspecies.
Until DNA sequencing became available, answering these questions was based more on intuition than on hard science. Even DNA seqeuncing doesn't fully resolve these ambiguities, because even identical plants have slightly different DNA. How different is different? The inevitable result is that many different scientific names are sometimes assigned to the same plant. This is what leads to plants like bluebells (Campanula rotundifolia), which have twenty scientific names!
Of course, only one name is considered current, but the others must be tracked as well. If you look up a cactus in an older reference book, you need to know how to associate the old name with the current one. So we list all the names, starting with the currently accepted name as defined by the USDA Plants Database. The first name listed has been simplified, by omitting the discovering botanists, following common convention. The second name listed is the first name, with botanists included. Any remaining names are older synonyms, in their full name format. This is a continuing process, so at any given time, the accepted name may be in dispute.
If you are curious as to how the names are assigned, see this Wikipedia article on the binomial naming system. Or take a look at the efforts underway to compile a single master list at the Missouri Botanical Garden in St. Louis and Kew.
Actually, plants don't just have two names; they also have names that place them in the family tree near their relatives. These full names express a place in the taxonomic tree by assigning a name to each major branch of the tree. This tree is in even more flux than the individual plant names, especially now that gene sequencing is telling scientists the real truth about plant relationships. So there are several taxonomies in vogue right now, and more to come. We currently use the ITIS (Integrated Taxonomic Information System) taxonomy.
But wait, there’s more! Horticultural names are a horse of a different color. Thanks to Michael McCarthy, who, writing in reference to the orchid Oncidium ‘Red Stars Rooster’, patiently explained a bit about how these rules work for orchids:
“Man made hybrids list this orchid have a grex name (e.g. Red Stars) which replaces the species. The grex should always be capitalized to distinguish it from a species, can be multiple words, and the genus and hybrid name are never italicized (be it a natural genus or a nothogenus). There is, additionally, a clonal name given here (‘Red Rooster’), meaning all of the plants being sold are clones of a particular plant that the nursery denoted as ‘Red Rooster’. As such, Wilsonara Red Stars ‘Red Rooster’, Oncidium Red Stars ‘Red Rooster’ and Oncidium Red Stars ‘Rooster’ are all valid names, with Oncidium being the currently accepted genus and Wilsonara as a valid synonym nothogenus. A brief summary of the ICNCP rules for naming orchids can be found here
“The species from which this was produced are known. The registration process requires that the parents of the cross be provided so that the lineage can be determined. In this case, the parentage is Oncidium Lisa Devos × Oncidium Issaka Nagatu and there are ten species that comprise its lineage (see: