I say potato, you say Solanum tuberosum

Guest post by Erin Fisher

What is Binomial Nomenclature?

Binomial nomenclature is also referred to as the latin or scientific name. Latin was at one time the universal (read: European) language of science. All scientific treatises were written in Latin. If you know your latin roots, looking at scientific names can be fun and can give you a clue for the common name or identifying characteristics of the plant: Toxicodendron diversilobum is poison oak.

The scientific method of naming plants is related to the study of taxonomy. Taxonomy is a systematic way of classifying all living organisms. Based on set theory, taxonomists group plants into divisions, families, genera, and species. The characteristics used to group plants have changed over the years. Flower characteristics, such as the number and placement of petals and male and female sexual organs, stem anatomy and genetic information are now used together to group species taxonomically.

Examples of characteristics that determine which division a plant is in: if the plant has a water and nutrient distribution system (mosses and worts don’t); if the plant has seeds (ferns don’t); if the plants have flowers (conifers don’t). Examples of characteristics that determine which family a plant is in: if genetic information indicates a common ancestor within the family (like people – if we have the same grandmother, we are family); flower petal and male and female sexual organ number and placement. Genera and species are often determined by the size of family characteristics – small petals versus large petals, long stamens versus short ones. Genera often have a wider range of sizes and species are, well, more specifically classified.

What is a Plant Species?

Generally speaking, plants of separate species are unable to interbreed. A species is also a group of plants that can be readily distinguished from other plants based on physical appearance but, because plants are so variable, species can be broken down into subspecies and varieties, because sometimes plants that look different can actually interbreed.

Binomial nomenclature refers to the two part name of each species. The first part of the name is the name of the genus and the second part is a modifier of the genus name that indicates the species. Toxicadendron is a genus name and can be used by itself to indicate a member of the Toxicadendron genus or can be used in combination with diversilobum to indicate the particular species within that genus. Diversilobum is only a modifier and is not informative by itself. There is only one genus called Toxicadendron but the species modifier diversilobum can occur in many genera.

Why Use Binomial Nomenclature?

Binomial nomenclature is useful because you don’t have to know what every species looks like to have a common botanical language. In my first plant taxonomy class, we learned to identify families by a gut feeling (or “gestalt” as my prof called it). Once you can look at a plant and know its family, it is pretty easy to use a key to figure out the genus and species. Thus, knowing families is actually more useful than memorizing every plant’s two part name. Many families have common characteristics such as flower petal arrangement (for example, a solitary flower with six petals not fused is typical of the Liliaceae or lily family) or reproductive organ arrangement (for example, four stamens, two tall and two short, is characteristic of the Brassicaceae or mustard family). For many common plants, you can know the genus by casual observation. For example: the genus Lupinus, or lupine (Fabaceae or pea family) can be apparent from the pea-type flowers arranged in a cone-like inflorescence and its distinctive leaves, but identification at the species level will take more investigation into the details of floral morphology. Some genera are more difficult to key to species than others and maybe it’s not even important which kind of lupine you’ve got. If someone tells you about a plant they have and you’ve never heard of the species, you can get a pretty good idea of what the plant looks like if the genus is familiar to you, even if the particular species isn’t. You do this all the time and may not even know it. Begonia is a plant genus name.

Why Not Use Common Names?

Common names can be easy to remember and, when talking to folks from your own region, useful. But if you just know a plant as ‘butter and eggs’, it can lead to miscommunication because there are lots of flowering plants with yellow and white petals known as ‘butter and eggs’. ‘Butter and eggs’ could be of the genus Ranunculus (family: Ranunculaceae or buttercup) or the genus Dendromecon (family: Papaveraceae or poppy). If you know which genus or even which family the plant belongs to, this knowledge can help you find the plant in a nursery or talk about it with other people. Common names can be more informative than ‘butter and eggs’ and still cause problems. For example, cactus is the common name for any plant with succulent leaves and spines. But plants have evolved this characteristic several times throughout history and there are several plant families with cactus plants within them. In Africa, cacti are commonly found in the Euphorbiaceae family – a family that also contains spurges and Poinsettia whose ovaries are above the flower petals. In South America, cacti are found in the Cactaceae family – a family that only includes succulents and whose ovaries are below the flower petals. While cactus is a useful term in describing appearance and growth habit, it is not useful in describing flower structure.

How Much Do You Need to Know?

The levels of classification that are relevant to most botanists are family, genus, and species. Tribes, or sub-families are also used to group genera in very large families such as Asteraceae (sunflower) and Fabaceae (pea). As you may have noticed, plant family names almost always end in -ceae. Genus names are a little more variable, but generally end in -us. Species names are all over the map. When you look at species names, they can sometimes tell you something about the appearance of the plant (example, variegata) or where it is found (example, gypsophilum, or gypsum-loving). Sometimes it is named after a person. A common species specifier in California is eastwoodii, after Alice Eastwood, a prolific and dedicated California botanist. Again, species monikers by themselves have very little information about plant identity – they are designed to only be used with genus names.


Binomial nomenclature can be intimidating to pronounce, but just remember your basic Latin: almost all consonants are hard and almost all vowels are long. There’s also room for your own interpretation: more than half of the California botanists I know pronounce -ceae (seee-eee), not (ki, long i). Most of us are not that hung up on a specific pronunciation. If anyone EVER gives you a hard time about your pronunciation, you are allowed to tell them to lighten up. Practice on your favorite plant names and starting getting familiar with the common plant families in your area. Once you get proficient at identifying members of the snapdragon family (for example), you’ll be able to identify plants that seemed really different, because of their different colored flowers or differently shaped leaves, as cousins.

For a database of flowering plant families and their characteristics (technical, text only) visit http://biodiversity.uno.edu/delta/

Erin is a restoration ecologist working in the San Francisco area.


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