The proper use of scientific names for plant species.

David H. Wagner --1999-- davidhwagner@compuserve.com

Every species of plant and animal should have at least one correct scientific name. This is the primary value of a scientific name: to provide a tag for a species that is consistent in the scientific community worldwide. Determining a correct name to use is the practice of nomenclature, a legalistic tradition that serves science. It is governed by a code of nomenclature kept current by regular international conventions. Learning to use the code and originating scientific names normally takes special training. However, using established correct names is not difficult. There are some simple conventions about the use of these names that every careful writer should learn.

The scientific name of a species is a binomial, composed of two words: a genus name and a specific epithet. Alnus rubra is the scientific name of the red alder so abundant in western Oregon. The first word (Alnus) is the genus name for alders and the second word (rubra, meaning red) is the specific epithet. A genus may have more than one species. In our area we also have the white alder, Alnus rhombifolia, mountain alder, Alnus tenuifolia, and the slide alder, Alnus sinuata. The word Alnus tells you that the species is an alder and the specific epithets define which species of alder you are talking about. But even a genus with only one species has a binomial for a name, like Ginkgo biloba.

A common mistake is to call the second name a species, as in, "genus and species." However, in the name for the red alder, rubra is not a species, it is merely a specific epithet. The same specific epithet may be used in used in many species names. Actaea rubra is the species name for the baneberry, in the buttercup family, while Festuca rubra is the species name for red fescue, a common grass. The binomial is the species name; a unique binomial defines the species. Another common mistake is to use "specie" when referring to a single species. There is no word "specie" in botanical terminology; in finance specie refers to coin, usually gold. Species is used the same way we use "sheep." The term for one species is the same as for many species. But when you want to talk about more than one genus note that the plural of genus is "genera" and not "genuses."

Because scientific names are in Latin, they are always italicized in typeset documents. Fortunately, this is quite easily done with word processors today. In typescript or handwritten documents the italicizing is indicated by underlining the scientific names. This is important because it helps somebody who does not know the language of the document to find the names of the species being discussed. An illustrated plant book in Russian, Polish, or Chinese is useful to anybody because the scientific names will identify the subject of the pictures. Also, it helps to distinguish between scientific names and common names. Often a common name is not the accurate scientific name: the common garden geraniums are actually in the genus Pelargonium while species in the genus Geranium are much less widely cultivated. It is a standard convention to make a common name by decapitalizing a generic name, translating the specific epithet, and using normal script. Thus, the common name of Penstemon fruticosus can be given as the shrubby penstemon. (I prefer to call these English names, since they are often not in common use.)

The genus name is always capitalized. In earlier times (up through the first half of the twentieth century) it was considered correct to capitalize specific epithets that were based on proper names or based on other genera, so in older literature you will encounter capitalized specific epithets. Now, convention dictates that all specific epithets are never capitalized.

In certain circumstances it is permissible to abbreviate the genus name of a species by using the first letter followed by a period. This can be useful when a species is discussed repeatedly. The first time a name is used it is always spelled out, subsequently it can be abbreviated. Alnus rubra can be referred to as A. rubra when it is mentioned later (but still on the same page or next--there's no standard convention on this). This can be done only when the meaning is completely unambiguous and no other species name beginning with the same letter is used in intervening text. If after mentioning Alnus rubra you talk about Actaea rubra, it is obvious that then writing A. rubra would be very confusing. The reader would not know whether an alder or baneberry is being referred to. Even if the specific epithet is different, do not abbreviate. For example, do not abbreviate Alnus if Abies procera is discussed after writing about Alnus rubra. Finally, if the species name begins a sentence, the genus should not be abbreviated but should be fully spelled out.

All species are classified into families, orders, etc., on up to division (or, in animals, phylum) and kingdom. The family is the most commonly used. Family names are made by adding "-aceae" to the end of the root of a name of a genus in that family. The family name for the maple family is Aceraceae (family names are capitalized but not italicized), from the genus Acer with the "-aceae" ending. There are six exceptions to this rule for making family names. These are traditional names going back to the time of the Greeks and Romans. The most common are the grass family, Gramineae, the parsley family, Umbelliferae, the mustard family, Cruciferae, and the sunflower family, the Compositae. There are accepted alternatives which have become more popular in recent decades--Poaceae for Gramineae, Brassicaceae for Cruciferae, Apiaceae for Umbelliferae, and Asteraceae for Compositae-but the traditional names are still proper to use. A common error in using family names is to write "Rosaceae family" when referring to the rose family. This is redundant, since the "-aceae" ending already tells you a family name is at hand and it is like saying "the rose family family."

There are a number of standard abbreviations involved with using scientific names. An unspecified member of a genus is indicated by "sp.," (like Alnus sp.). This is often used in inventory work when somebody knows the genus of a plant but not the exact species. Reference to more than one species is abbreviated, "spp." (like Alnus spp.). The "sp." and "spp." are not italicized. Do not confuse these with the abbreviation for subspecies ("subsp." for singular and "subspp." when referring to several subspecies). There are some handy fudge words that are usually used in abbreviated form: s.s. for sensu stricto and s.l. for sensu lato. The abbreviations follow the name being modified (like Alnus incana s.l. and A. incana s.s.). These abbreviations are italicized since they abbreviate Latin phrases. The first, s.s., means "in a narrow sense" and s.l. means "in a broad sense." The s.l. is handy when you know a species has been divided up into a number of more narrowly defined species by some authorities and you want to refer to the related species in the broad sense, including them all under one name. This notation implies that you know about the more narrowly defined species and are deliberately not recognizing them. The same sort of treatment can occur with genera. Berberis s.l. includes both barberries and the Oregon grape, while Berberis s.s. would imply that you recognize placing plants like the Oregon grape into another genus, Mahonia, and keep only the barberries in Berberis.

A favorite appellation is vel aff. attached to the end of a name. It is the abbreviation of a Latin phrase that means "or something related to this" and allows you to designate a species name while admitting your lack of confidence in that designation. Identifying a fern as Botrychium lunaria vel aff. means you know it's one of the moonworts but you're not sure you can tell the moonworts apart so you are using the species name of the first named, most widespread one as a tag. This is different from s.l. because with vel aff. you are allowing that the name you are using may be the wrong one. This is just as close as you can get.

Instead of dividing one species into several species, it often makes more sense to treat minor forms or geographical races as units below the rank of species. These are then given infraspecific names, the most common of which are subspecies and variety. Normally, only one or the other is used but sometimes a species has such a complex genetic structure and/or wide geographical distribution that a species will be divided into subspecies and the subspecies divided into varieties. Each of these is given an epithet, in the format, "Species subsp. subspecies," "Species var. variety," or "Species subsp. subspecies var. variety."

When writing a list of names, it is standard convention to alphabetize them. Often a reader is interested in only one or a few species and it helps to find the species of interest if they are alphabetized. If a long list is involved, it is often broken down by first grouping the species into families and alphabetizing the families, then alphabetizing the species within the families. Other kinds of categories besides families may be useful for organizing lists, such as trees, shrubs, and herbs.

In formal scientific writing for professional journals the first time a name is used it should include more than just the Latin binomial. A complete scientific name includes reference to the author(s) of the name. The authors are usually abbreviated with a standard abbreviation. Linnaeus is abbreviated as "L." In botanical nomenclature, two authors will be mentioned if the name used by an original author has been changed because of a change in classification. For example, the common sword fern was first described as Aspidium munitum by a botanist named Kaulfuss. The full name of the sword fern was then Aspidium munitum Kaulf. Later, a botanist named Presl published a document where he placed the sword fern into a different genus, Polystichum. This classification is the one accepted today as the correct name, so the complete name we use is Polystichum munitum (Kaulf.) Presl. The describing author is placed in parentheses followed by the combining author. Each infraspecific epithet also has its own author (and combining author) except the typical form which just repeats the epithet of the rank just above. Thus, we have Polystichum imbricans (D. C. Eat.) D. H. Wagner subsp. imbricans and Polystichum imbricans (D.C. Eat.) D. H. Wagner subsp. curtum (J. Ewan) D. H. Wagner. (Note that in names of animals the treatment of combining author is different. If an accepted species name of an animal is in a genus different from that of the describing author, the describing author's name is put in parentheses but no combining author is mentioned. If the accepted species name is the same as the original, no parentheses are present.) Not all journals require listing of authorities with names, but will permit you to cite a standard, general reference whose nomenclature you follow.

David H. Wagner
Northwest Botanical Institute
16 June 1999