Scientific names of plants have two words, the genus name and the species name, often called the specific epithet. The scientific name, with two words, is also called the “binomial.” The goal of plant identification., besides recognizing a species, is to determine its accepted scientific name. For example, Serenoa repens is the accepted scientific name of what is commonly called saw palmetto. Serenoa is the genus name and repens is the specific epithet. Both words are Latinized.
Before modern botany, people lived in isolated tribes. We informed one another where we could find good plants in our region that we could safely eat. Or harvest for medicine or clothing. Or make into snares and weapons. Or build our huts. Plant identification skills, including naming plant species, were based on comparison with related or similar species according to their morphological shape or size or color. Not surprisingly the “kind” of plant recognized traditionally by its “common name” is often the same as the species recognized in modern taxonomy by its scientific name. So, the concept of a species is often the same, just under a different name.
Common names
Common names in local dialects helped for millennia in communication but are not part of framework for international systematic taxonomy. There are many practical advantages of an organized system that is aloof from daily local communications in the marketplace, and that is not tied to regional dialects, and that can be used across tribes and boundaries.
Common names are sometimes applied to more than one species. One species can have multiple common names. But scientific names are intended to be just one accepted scientific name for one species, and each species should have only one accepted binomial or scientific name. When there are discrepancies or conflicts, international rules of nomenclature resolve such conflicts by going back to the earliest published use (“priority”) of a species name. And rules of nomenclature are flexible to make orderly changes and corrections. When there are changes in concept of species, the species can be formally transferred to another genus, preserving the original concept while recognizing a change in relationship.
“Specific epithet”
It can be confusing that the “species” is the entity being identified and named, and the second word in the binomial is called the “species name” or the “specific epithet.” This is because without a genus name, the second word, the “specific epithet,” does not refer to any one thing. It can refer to different things.
For example, the specific epithet “repens” in the binomial “Paspalum repens” is repeated in other binomials such as Serenoa repens and is not used by itself. The specific epithet “repens” is just Latin for “creeping” or “crawling.” And more than one species can be “repens,” if they occur in different genera (plural for genus.) Therefore, to be clear, a binomial or scientific name is not a genus and a species but is a genus name and species name or specific epithet.
Plant genus names are not recycled. There is only one Paspalum and one Serenoa. So it is okay to use a plant genus name by itself as representing all the species within that genus, such as Paspalum notatum, Paspalum repens, and Paspalum vaginatum. For shorthand, after first mention, the genus name can be abbreviated, e.g., Paspalum notatum, P. repens, and P. vaginatum. And if we don’t know which species of Paspalum we are observing, we can just call it “Paspalum sp.” (And if we want to refer to several species of Paspalum without naming them all, we can say “Paspalum spp.” or if we want to refer to a subspecies of Paspalum notatum we can say Paspalum notatum subsp. notatum.
Scientific names are commonly written as italic letters or sometimes they are underlined. This is a typographical style that may be good on the eye for readers or may be required by editors. But italics are not required in botanical nomenclature.