4 Introduction to Binomial Nomenclature
Learning Objectives
- Employ correct naming and plant identification terminology.
For an orderly system of classification, botanists give each group of plants a name that is recognized by people who know binomial nomenclature, regardless of where they are or the language they speak. This way every plant species will have a unique botanical name based on the binomial system of nomenclature. For example, one of the best-known trees of the Pacific Northwest, the Douglas fir, recognizes botanist Archibald Menzies in its scientific name Pseudotsuga menziesii. While the common name recognizes fellow botanist David Douglas, Archibard Menzies is credited with the first botanical description of the plant.
A plant name or binomial is made up of two names: a genus name and a (usually) descriptive specific epithet (species name), both commonly of Latin or Greek origin. For example, of the many species within the group known as pines (genus = Pinus) there is only one named Pinus contorta (contorta = twisted). This species is characterized by often having contorted or twisted young shoots. The “species name” is the binomial; for instance, the species to which we belong is Homo sapiens.
Genus
A genus (plural = genera) is defined as an assemblage consisting of one or more related species that are more like each other than to other species, and that includes the entire surviving lineage of the ancestral population. Evidence for these relationships is deduced from the fossil record and from comparative techniques in morphological, chemical and molecular (DNA sequencing) analysis.
A genus name can be descriptive of the plant, such as Equisetum (common horsetail) which is from two Latin words equus (horse) and saeta (bristle). The genus can be the actual Latin or Greek name such as Erysimum which is derived from the Greek name for the same plant erysimon. It can also be derived from the plant founder’s name such as Davidia, which is from Father David, a famous French plant explorer who lived in China for many years.
Species
The species is the basic life-unit in biology and can be defined as consisting of one or more related species that are more like each other than to other populations and that presumably come from a single ancestral population. The species name may be an adjective that indicates a distinguishing characteristic of the species, e.g., Quercus alba – white oak, or a noun that honors a person or indicates the species habitat. Species is abbreviated sp. (a single species) or spp. (more than one species).
Subspecies
Subspecies (ssp. or subsp.) and variety (var.) names are also multinomials. For example, lodgepole pine is known by the botanical name Pinus contorta var. latifolia, or sometimes, P. contorta ssp. latifolia. In other words, a northern variant of Pinus contorta with needles more flattened (lati = broad and folia = leaf) than the typical, coastal variety (P. contorta var. contorta). Note that “variety” is used here at the same rank as “subspecies” while some botanists consider the “variety” as a lower rank. These terms are used to describe naturally occurring plants.
Form
The rank form or forma (f. or fa.), is used to represent individuals which differ in some specific way from other individuals within the same natural populations. For example, one can find numerous red bract forms throughout populations of the more commonly white bract Cornus florida (Eastern flowering dogwood). These red bract dogwoods are correctly known as Cornus florida f. rubra (rubra = red). Other common, naturally-occurring mutations in other plants include: weeping habit (f. pendula), dissected leaves (f. dissecta), and white flowers (f. alba).
Hybrids
Hybrids are the offspring of successful mating between plants belonging to different taxa. Known interspecific hybrids (between species in the same genus) are designated by a multiplication sign, as Platanus × acerifolia (P. occidentalis × P. orientalis). Intergeneric hybrids result from crossing plants belonging to separate genera; an intergeneric hybrid name is always preceded by a multiplication sign, as ×Solidaster (Solidago × Aster).
Cultivars
Cultivars are horticultural races or strains of plants which originate under cultivation or may originate in nature as a mutation and subsequently persist under human cultivation. The word cultivar (cv.) comes from “cultivated variety,” a somewhat confusing derivation, since the “variety” represents a naturally occurring entity, while the cultivar does not.
As cultivars do not persist in nature, it is not a botanical designation; however, where used, the cultivar is considered part of the botanical name and must be appended to it. Cultivar names are distinguished in text using single quotation marks, as Chamaecyparis pisifera ‘Filifera Aurea’ (filaments or threads of gold).
Common Names
Common names are the local, familiar names given to plants. The same common name may be used for several completely different plants. For example, the common name “cedar” is a name given to a variety of plants with aromatic wood (recalling the “cedar” of antiquity, Cedrus spp.) or to plants that are reminiscent of other plants called “cedars,” for example. In the Pacific Northwest, cedar refers to Thuja (western red cedar) and to Cupressus (yellow cedar).
Similarly, a single species may have numerous common names, particularly if known from a variety of locations. For example, yellow cedar is also known as Nootka cypress and Alaska cedar. Clearly, there is potential for much confusion with common names. In text, common names are written out in lower case, except where they include proper names; e.g., Douglas fir, Japanese painted fern, etc. Common names are not botanical names. While botanical names are often, at least initially, difficult to remember and pronounce, they are universally recognized and considerably more accurate than common names.