Binomial Nomenclature

Plant Taxonomy

by Joelle Steele

If you've been working with plants for awhile you probably already know how confusing all of those Latin plant names can be, particularly if you don't really know what they mean or what they stand for. This article will try to simplify the process of plant classification and help you understand how the system works while giving you a little insight into how the names should be properly pronounced.

TAXONOMY

Taxonomy is the science of the classification of organisms, in this case plants, into categories which are based on common characteristics. This taxonomic system is called the International Code of Botanical Nomenclature (ICBN) and was invented by Swedish botanist Carl von Linne (known more commonly by the Latin form of his name, Carolus Linnaeus). It was first published in 1753 and it is revised periodically to help eliminate errors or confusion, which can arise due to misunderstandings or misidentifications, and to insure that new plants are properly classified. This system for naming a species using a generic name and a specific epithet is called binomial (meaning two names) nomenclature (meaning naming method).

The following is an explanation of the hierarchy of taxonomic ranks beginning with the largest and highest level of classification, the kingdom, and ending with the smallest levels of species and their hybrids and cultivars.

KINGDOM is the highest level in taxonomy. Traditionally all living organisms are placed in either the Plantae (plant) or Animalia (animal) kingdom, though in recent years other kingdoms have been suggested for certain kinds of fungi and unicellular organisms.

PHYLUM or DIVISION, is the category of the highest magnitude within a kingdom. The Latin names of divisions begin with a capital letter and end in -phyta, such as Spermatophyta (seed-bearing plants), and Pteridophyta (non-seed-bearing vascular plants). The plural of phylum is phyla.

CLASS or ASSOCIATION, is a category consisting of plant communities within a phylum. Each class consists of similar vegetation which have certain characteristics in common. The Latin names of classes begin with a capital letter and end in -etum.

ORDER is a major category in the taxonomic hierarchy and is composed of groups of families. Groups of similar orders are placed in classes and the Latin names of orders begin with a capital letter and end in either -ales (Rosales or Geraniales) or in -ae (Rosae or Tubiflorae).

FAMILY is also a major category which is comprised of groups of similar genera. Families represent the highest natural grouping. Their Latin names are capitalized and end in -aceae, with eight exceptions which end in -ae (such as Leguminosae and Palmae). Some of our most widely used interiorscape plants belong to the families Araceae (aroids), Bromelioideae (bromeliads), Moraceae (figs), and Palmae (palms).

SUB-FAMILY is a classification which consists of similar tribes.

TRIBE is a term applied to groups of similar genera within a large family. Their Latin names are capitalized and end in -eae.

SUB-TRIBE is a classification which consists of similar genera within a tribe. The names are capitalized and end in -inae.

GENUS is a group consisting of homogeneous species. The generic name forms the first part of the Latin binomial name and is usually singular, capitalized, and lacking a uniform ending. Collections of similar genera are grouped into families. Large genera such as Rhododendron may need to be further divided into smaller groups called sections, series, subgenera, subsections and subseries. Genera is the plural form of genus. The name of a genus is written in italics and is usually followed by the name of a person (the author). If the author name follows a species or subspecies it indicates the person who proposed the name. If it is in parenthesis it means that the species or subspecies was originally placed in a genus other than the present one. Our popular dracaenas actually come from three genera: Dracaena proper, Pleomele, and Cordyline.

SPECIES is the fundamental unit of study in taxonomy. The specific epithet forms the second part of the binomial name and is always written in lower case, such as fragrans massangeana, reflexa, sanderiana, and marginata. The ending always agrees with the gender of the generic name.

SUB-SPECIES is a group consisting of several biotypes which are a form of a species, usually defined by geographical region or range. For example, subspecies may share a common origin and possess many similar characteristics with only slight differences owing to their regional location. The name of the subspecies which includes the type is always the same as the specific epithet.

VARIETY is a category which consists of morphological variants which may or may not have a specific geographical distribution. For example, a variety may exhibit a difference in color.

FORMA or FORM is the lowest rank normally used and it is used to distinguish variants of subspecies and varieties, usually by a characteristic such as albino flowers occurring within a population of colored flowers.

SPORTS are atypical forms of an individual or part of an individual due to mutation or segregation.

CULTIVAR stands for a CULTIvated VARiety which was produced by scientific techniques that do not usually occur in nature. Cultivar names are capitalized and written within single quotes, as with 'Warneckei,' 'Silver Queen,' or 'Mauna Loa.'

HYBRIDS are plants that are produced from genetically different parents from the same or different species. Hybrids which are bred from different species are often sterile. Those produced from within the same species are usually vigorous plants but may pose difficulties for commercial growing because they do not always breed true. You can recognize a hybrid name because it consists of two species names linked by an "x," such as Philodendron x 'Wendimbe.'

COMMON NAMES are those which are usually written in English or some language other than Latin such as Chinese evergreen which is the common name for the scientific name Aglaonema.

To give you an idea of how this system would apply to one of our indoor plants we will take our ever popular Marble Queen Pothos. It belongs to the family Araceae which consists of aroid plants such as philodendrons. It belongs to the genus Scindapsus and its species name in binomial nomenclature is Scindapsus aureus (aureus meaning golden). Its cultivar name is 'Marble Queen,' hence its entire botanical name is Scindapsus aureus 'Marble Queen.' Rubber trees belong to the family Moraceae (the figs), genus Ficus, species name Ficus elastica, and cultivar name 'Decora,' thus, their full name Ficus elastica 'Decora.'

PRONUNCIATION

Pronouncing botanical names can be a challenge to those who have not studied Latin. It is even a challenge to those of us who have, since scholars do not agree on which version of Latin to use. In this article we'll depend on the most often used version, that of the 14th century. In spoken Latin, the vowels are pronounced: a as in fall, e as in set, i as in pin, o as vote, u as in full, y in phyllus as in the word due.

Latin has "diphthongs" which are two-letter pairs which combine to make a slightly different sound. These letters are enunciated separately: ae sounds like ah-eh, ai sounds like ah-ee or eye, au sounds like the ou in house, ei sounds like the ei in eight, eo sounds like ee-oh, eu sounds like eh-oo, ie sounds like ee-eh, oi sounds like oh-ee, iu sounds like ee-uh or like ee-oo, ue sounds like oo-eh or uh-eh, ui sounds like oo-ee, and oe sounds like oh-eh. Perfect diphthongs, such as ae and oe, are sounded like a vowel that is midway in sound between the two, for example, the ae in Linnaeus or the oe in coelestis.

What's left? The consonants. Using 14th century Latin, c is pronounced like a k when it precedes a, o, or u and is pronounced like an s or z when it precedes ae, e, i, oe, or y. The letter g is hard when it precedes a, o, or u and becomes a soft j sound before e or i.

To properly pronounce these names you must also place the emphasis on the proper syllable. For two or three syllable names the accent is usually on the first syllable. Words with more than three syllables have the accent on the next to last syllable. Many names are not pronounced this way owing to common usage, but, this is, scientifically and scholastically, the correct pronunciation.

Some plants are not Latin or Greek based and may come from another language entirely, such as the "kalanchoe." How do you pronounce it? Is it "KAL-AN-KO" or "KAL-AN-KO-EE"? Surprise, it's neither! It's Chinese and is pronounced "KAL-AN-CHO-EH," with the emphasis on the second syllable.

Learning to classify plants and pronounce their names properly reduces the confusion that arises from relying on common names and from mispronouncing names to such an extent that growers do not know what you are talking about when you ask for it. In addition, knowing this scientific aspect of horticulture enables us to demonstrate our expertise with plants each time we open our mouths!