PBIO 250 Lecture Notes
James L. Reveal
Norton-Brown Herbarium, University of Maryland
One of the stated goals of systematic botany is that each organism shall have one, and only one, correct scientific name. For many individuals who have cause to use scientific name it seems that this is never the case. Names seem to change all the time, creating a sense of confusion, and often leading to expensive changes in laws, international treaties, and other business dealings.
The truth is that the vast majority of plant do indeed have one and only one correct name, but what many fail to realize is that this applies only to binomial or trinomial, that is, the combination of a generic name and species epithet (binomial) or, if appropriate, an additional infraspecific epithet (trinomial). The name Eriogonum umbellatum is a binomial; Eriogonum umbellatum var. majus is a trinomial.
The usual statement of "one and only one correct name" needs to be modified to "one and only one correct name at a given rank" to be more accurate. For example, the taxon known as Eriogonum umbellatum var. majus, if regarded as a species must be termed Eriogonum subalpinum. It is the same plant only the rank is different. It can be even more difficult: Eriogonum umbellatum var. subaridum is the same thing as Eriogonum umbellatum subsp. ferrisii and Eriogonum biumbellatum. In short, this plant can have three different names, each one of which is the one and only one correct name at each of the three fundamental ranks: variety, subspecies and species.
Names change for two basic reasons: new evidence requiring a change in position or circumscription of the taxon, or for technical nomenclatural reasons when the name can be shown not to be the correct or even available name at the rank in question.
Science is not static so it should come as no surprise that botany, a branch of science, should have fields within it that produce new scientific evidence that causes previously expressed opinions to be altered. The plant initially named Chorizanthe insigne was thought later to be a member of the genus Centrostegia and the combination Centrostegia insigne was proposed. The name was change because new evidence indicated that this species did not belong in Chorizanthe but rather in Centrostegia. Recently, this species was examined again, and it was decided that the taxon belong to neither genus, but to a genus of its own, and the name Aristocapsa insigne was proposed in 1989.
Change of this sort will always occur. Note that in this case, the specific epithet remained the same but the circumscription of the genus changed. Specifically, Chorizanthe was broadly defined initially to include species that were transferred to a new genus, Centrostegia with a new definition, or circumscription, of Chorizanthe resulting. When Aristocapsa was established, Centrostegia was redefined so as to exclude from its circumscription the taxon insigne.
Occasionally, when a taxon is recircumscribed, the resulting names are new. When Linnaeus described the common dandelion in 1753, he placed the plant in the genus Leontodon, calling it L. taraxacum. Weber, in 1780, altered the circumscription of Leontodon by excluding dandelion and placing it in its own genus, Taraxacum, giving a new epithet so that the correct name of dandelion is Taraxacum officinale.
The scientific name for tomato differs according to its position. In Solanum, its correct name is S. lycopersicum, but if the name is positioned in the genus Lycopersicon, the correct name is L. esculentum.
Many names are changed for purely technical reasons having to do with provision in the International Code of Botanical Nomenclature where there are rules that require a name to be published in a certain way, and where the concept of priority governs which name, among competing names, must be used. The latter provision is in the Code so as to remove personal biases in the selection of any name.
A century ago, the scientific name of Douglas fir, an economically important lumber tree of the Pacific Northwest, was Pseutotsuga taxifolia. Fifty years ago the tree was called P. douglasii. Now it is known as P. menziesii. Same tree, three different names. The specific epithet "taxifolia" was not correct because that name had been used earlier for another plant and the Code requires that the second name be changed; it was, to "douglasii". Unfortunately, there was an earlier name, "menziesii, and it had priority over "douglasii" and therefore the earlier name had to be adopted.
Over the last half of the 20th Century, the systematic community has worked to reduced the number of nomenclatural-based changes by altering the Code to permit conservation of names at the genus, family, and most recently, species ranks. Recently it has become possible to reject any name (at any rank) whose adoption would result in nomenclatural instability. A growing list of works (entire or in part) have been excluded by international agreement so as to reduce nomenclatural confusion. Additionally, new provisions in the Code permit the conservation of a type so as to prevent an alteration of the application of a name because the name was circumscribed so as to include its own type element.
In 1753, Linnaeus decided to apply the name Caryophyllus to a group of tropical plants of the family Myrtaceae, and establish Dianthus for a temperate herb long know to pre-1753 botanists as Caryophyllus. In spite of this, post-1753 authors continued to use Caryophyllaceae as the family name for the group of plants that contained the genus Dianthus but exclude the genus Caryophyllus. For the family name to be used, Caryophyllaceae has been conserved.
Calycanthus was proposed by Linnaeus in 1759. Unknown to him the same genus had been established earlier by Philip Miller in 1755 who called it Basteria. No one used Basteria after 1759 (not even Miller) but as this name had priority, it was necessary to conserved Calycanthus for it to be the correct name for the genus.
Cassia galegifolia was proposed by Linnaeus in 1759 based on a Plumier plate published in 1756. The exact identity of the plant figured by Plumier was never establish by any monographer of the genus Cassia, yet, in 1988, Lourteig concluded the figure represented a plant of Senna pallida, a name proposed by Vahl in 1807 and used since that date. Senna pallida is an exceedingly variable plant, with Irwin and Barneby, in 1982, recognizing some 19 varieties for this tropical American plant. To prevent adoption of the Linnaean name, which had not been used previously, and to avoid making numerous new combinations, Cassia galegifolia was proposed for rejection in 1992 and this was accepted in 1994.
A series of encyclopedia articles written by English naturalist John Hill, and published from 1753 until 1756, were "discovered" in 1990. Numerous new genera were published, many of major economic importance, but with names soon published thereafter by other authors. For example, Hill proposed Abies, the generic name for fir, in October of 1753, and Philip Miller proposed the same name on 28 January 1754. Without exception, Abies has been attributed to Miller. To avoid the need to alter even authorships, the works of Hill were excluded from nomenclatural consideration so as to reduce the likelihood of confusion.
One of the more common eastern North America composites is Hieracium gronovii whose circumscription excluded the element used primarily by Linnaeus in 1753 to establish the name. That element, a Pehr Kalm collection found in Linnaeus herbarium, upon study proved to be a specimen of H. venosum. As H. gronovii had been use in a sense so as to exclude its type (the Kalm collection) without interruption for over 200 years, the name was proposed for conservation in 1992 with a new type specimen, a Clayton collection from Virginia. This recommendation was accepted and the name H. gronovii remains in use.
The systematic community is in the process of considering the establishment of a series of official lists of scientific names which will be "protected" (e.g., can not be altered for nomenclatural reasons). In 1993, listings of family and generic names were published, but changes to the Code to put such lists into effect were narrowly defeated. The question will be considered again in 1999.
A related effort is the proposal to establish a "biological code" of nomenclature. While the efforts has merits, many object to having an additional code. For more information see Proceedings of A Mini-Symposium on Biological Nomenclature in the 21th Century.
Scientific names will continue to change for a variety of reasons. The best one can hope for is a reduction in the alteration of commonly used names strictly for nomenclatural reasons. It will require work and good judgment on the part of botanists, and understanding on the part of those who use scientific names, to make the future of botanical nomenclature more stable.