Classification, identification, nomenclature


Classification schemes are an attempt to place plants in categories that are useful to the individual doing the classifying. Because there is considerable diversity in the way in which plants are used, as well as the appearance of plants, there are many different plant classification systems. For botanists, however, the only universally accepted scheme for plant classification is one that attempts to show genetic (phyllogenetic = evolutionary) relationships among plants.


Classification assumes that members of any given group have more in common with one another than with members of any other equivalent group. Instead of having to record and remember separately the features and properties of each individual within a group, we need only concern ourselves with those of the group as a whole, knowing that the characters will apply to all members. E.g. any apple has more in common with any other apple than it does with an orange, or a pear.


Classification, loosely, is the assignment of like-objects to recognizable groups. It facilitates reference to them and transmission of information about them.


Need for classification

          The numbers of different kinds of plants are exceedingly great. An estimated 300,000+, and if we include the fungi (molds, mushrooms, toadstools), then about 450,000 different organisms. The plant kingdom is large and diverse. It is an impossible task to record and remember the character and properties of each one of these plants, individually. Some kind of grouping and summarizing is essential for us to begin to understand and utilize the vegetable world. Size and diversity of plant kingdom makes classification necessary


Identification – the recognition of sameness. This is a basic process of classification; the process of deciding whether or not two things are, in your opinion, the same. It is not the same as naming.

In classifying plants, we use our judgment to decide which plants should form groups of similar individuals. Each identification we make in doing this involves an act of judgment on our part. A classification, then, is built up by a series of such acts of comparison and judgment: we ask ourselves ‘are these two the same or are they different?’ Each time we classify a new plant into a group which we have already established, we carry out an act of identification – ‘yes, this is the same as those’.


Taxonomic ranking - each ranking up the taxonomic hierarchical ladder - from species to genus to family - shows an increasingly greater range of variation. The lower the rank of a taxon (general term for any taxonomic rank: species, genus, family, etc.), the fewer are its members and the more they have in common with one another; the more detailed the classification becomes and the more particular is the information about the plants concerned.

As one goes up the taxonomic hierarchical ladder, the rankings become increasingly more inclusive; they draw in more taxa because they allow for greater variability.  


Taxonomic hierarchy


Species - plants of one kind, e.g. "cinnamonea.

Genus - group of related species, e.g  Rosa.

Family - group of related genera that share combinations of morphological shapes, especially floral and fruit features. e.g. Rosaceae. (Family names are capitalized, and usually end in _aceae.)

Order - group of related families. E.g. Rosales. (Capitalized and ends in _ales.)

Class - group of related orders. Dicotyledoneae (as opposed to Monocotyledoneae).

Subdivision - group of related classes. Angiospermae (as opposed to Gymnospermae).

Division - group of related subdivisions. Spermatophyta (seed plants), as opposed to Thallophyta (algae), Bryophyta (mosses and liverworts), Pteridophyta (ferns) and fern-allies, etc.

Kingdom - Plantae


Each ranking up the taxonomic hierarchical ladder, from species to genus to family, shows an increasingly greater range of variation; more inclusive.

The lower the rank of a taxon (general term for any taxonomic rank: species, genus, family, etc.):

a.      the fewer are its members; the more exclusive

b.     the more they have in common with one another.

c.     the more detailed the classification becomes (the tighter the relationship).

d.     the more particular the information about the plants.


Example: We have a plant, Senecio vulgaris (groundsel) visible to us, in front of a screen. We have another plant hidden from us behind the screen.

a.      If we are told the hidden plant is also a Senecio vulgaris (the same species), we can predict that the hidden plant will look very much like the plant in front of the screen. It will share many of the same characters as the visible plant, and without seeing the hidden plant, we’d be able to describe it. There might be slight genetic difference as to the height of the plant or the robustness, but it will be appreciably the same as the visible plant of the same species.

b.     If we are told the hidden plant is in the same genus as Senecio vulgaris (Senecio sp.), we can still predict a great deal about the hidden plant, but not as accurately as we could with the plant of the same species. There may be hundreds of different Senecio species, and even though they may all share a considerable amount of attributes, there will still be greater variation than there was with the same species.

c.     If we are told the hidden plant is in the same family as Senecio vulagaris, the composite family (Asteraceae), we can predict even less. There are over a hundred different genera (plural of genus) in the family, and each genus may have between one and hundreds of species within its rank. Now, there are thousands of plants to choose from and the shared characters are less and less. We can probably predict the fruit type will be an achene, but little else.

d.     If we are told the hidden plant is in the same order as Senecio vulgaris (Asterales), we can predict less still about the hidden plant. On top of the thousands of plants that share some general characters with Senecio vulgaris, the order, Asterales, are composed of even more families, such as Campanulaceae and Dipsacaceae.

e.      And so on and so forth, up the hierarchical ladder to class, subdivision, division, and kingdom, each succeeding rung in the hierarchy becoming less predictive because there are fewer and fewer shared characters with the individual Senecio vulgaris, the plant with which we began.


Scientific names - The part of systematic or taxonomic botany that deals with the giving of names to plants is referred to as nomenclature. The purpose of a name is to act as an easy means of reference, as an aid to communication.

1. Names impart some information about a plant: flower color, leaf shape, flavor, location, season of blooming and, especially, relationships.

2. This is true of all names, such as your own first names and surnames, not only of scientific names of plants.

3. The use of a name avoids the use of a descriptive phrase every time we wish to refer to an object, or group of objects. It is easier to say “I saw some bluebells in the woods today” than it is to say, “I saw some plants with blue elongated bell-shaped flowers in groups at the ends of long stalks and with parallel-sided leaves about a foot long, all springing from ground level in the woods today”.

4. To some extent, however, that is how plants had previously been referred. A name, then, stands, as it were, in place of the object itself and acts as means of reference to it.


By the time Linnaeus came along and wrote his famous and influential treatises, Genera Plantarum (1737) and Species Plantarum (1753), plants were described in a polynomial system of nomenclature. Polynomials included a single word for a plant (what we now refer to as a genus), followed by a lengthy list of descriptive terms in Latin.

 E.g. Ranunculus calycibus retroflexis, pedunculis falcatis, caule erecto, folius compositis. Roughly, it means, the buttercup with reflexed sepals, curved flower stalks, erect stem, and compound leaves.

Polynomials were not standardized, different polynomials existed for the same plant, and was cumbersome to remember.

One of Linnaeus’ great accomplishments was to introduce, almost inadvertently, a binomial system of nomenclature, or the 2-word scientific name. (The binomial system is now used for all known organisms). He used this system of reference consistently in Species Plantarum, a work which describes and names 5,900 plants, all the plants known to Linnaeus.

The binomial system simplified scientific names. In 1867, a group of botanists at the International Botanical Congress in Paris established rules governing plant nomenclature and classification. They established Species Plantarum as the starting point for scientific names and, thru the International Code of Botanical Nomenclature, formalized and standardized  plant naming procedures and rules.


Scientific plant names must be in Latin.

          1. This overcomes the difficulty of multiplicity of different languages which makes common names confusing and unsatisfactory.

          2. Latin was the common language of learned men in Europe, where formal botany originated and developed. Linnaeus himself was born Carl von Linne, which he Latinized to Carolus Linnaeus, a practice common among scholars of the time.

          3. Latin is essentially a “dead” language - that is, it is no longer spoken as a native tongue by any people, avoiding elements of national bias and jealousy, and words are no longer being added or subtracted to the language. (It has a stable glossary and grammar).


Of what is a scientific name composed?


Each kind of organism is known as a species, and similar species form a group called a genus. Each species has a scientific name in Latin that consists of two elements: the first is the genus and the second is the specific epithet. Together they are referred to as a binomial (literally - 2 names), and is always either italicized or underlined.  

Binomial - the binomial is comprised of a genus and a specific epithet.

1.                        Genus - the first word in a binomial, is always a singular noun, written with a capitalized initial letter - Rosa.

2.                        Species - made up of 2 parts: genus and specific epithet. Rosa woodsii. Specific epithet is not capitalized (lower case).  It is usually an adjective (angustifolia) or named after a person (walkeri), a commemorative, or place (nevadensis).Altho the generic name can be used by itself to refer to several species within the genus, specific names by themselves are not sufficient; they have no independent meaning, and cannot refer to a specific plant. E.g. “japonica” from Arbutus japonica, means only “Japanese”. It does not refer to a particular plant. Many plants may bear the specific epithet of “japonica”. Epithets, then, are meaningful only in combination with a generic name.

Binomial - generic name (genus) + specific epithet. It provides a summary of affinities which acts as an aid to memory, and enables one to make inferences about plants unknown to us. E.g. groundsel or Senecio vulgaris and Oxford ragwort or Senecio squalidus. If we are familiar with the groundsel but not the ragwort we can, nevertheless, infer, since both are species within Senecio; they share common characteristics.

The binomial grouping reflects natural relationships based on shared vegetative and reproductive characteristics.

          Our names are, essentially, binomials. In the phone book we are listed last name first. Our last names (surnames) act as genera : Lennon, for example. Which Lennon? John Lennon describes which Lennon we are referring to, and distinguishes him from Robert Lennon, Sally Lennon, and Roberta Lennon. Altho, all very similar genetically, they each represent very particular expressions of self that are different from one another.


Citation of authority - refers to the first person who validly published the name, or first described the plant, or who first placed the plant in a particular genus.. E.g. Primula vulgaris Huds. Or, Zea mays L. Authority names are often abbreviated and, when in reference to Linnaeus, abbreviated with only the first letter of his last name, L. The authority is not part of the botanical name but is often added for purposes of precision.


A scientific name is unique in that it refers to only one species and is universally accepted among scientists


. Trinomial - refers to the rank below that of species - subspecies or variety. A plant group can be so different in the wild from the general species originally described,  that it warrants a botanical variety classification below that of species. E.g. Buxus microphylla Sieb. and Zucc. var. japonica Rehd. and Wils., which is native to Japan, and Buxus microphylla var. koreana Nakai, which is native to Korea. “Var.” stands for varietas, Latin for variety. These botanical varieties are sufficiently different to warrant unique names and authorities to distinguish them from one another.

          Cultivars are cultivated varieties, a term used in both agriculture and horticulture (a contraction of cultivated variety). If propagated by vegetative means they are referred to as “clones”; if by seeds they are referred to as “lines”. Cultivar is abbreviated as cv. It is often a distinct variant selected by someone who believed it was uniquely different from any plant already in cultivation. Could refer to a difference in flower color, spines vs. no spines, etc. (The cultivar name is always capitalized but never underlined.)



Common names (vernacular names, familiar names) - common names are very often descriptive and poetic references to plants.  However, a common name may refer to more than one plant or, conversely, many plants may have the same common name. Common names are often ambiguous and often regional or local, rarely universal.

          E.g. Bird of paradise may be Strelitzia reginae, from the Strelitziaceae, a monocot from the tropics. But in the North American southwest deserts, Bird of paradise refers to Caesalpinia gilessii, a leguminous dicot from the Fabaceae.

          Or the very same plant, say Arbutus unedo, may be known by different common names, depending on geography or language:  Osage orange is also known as bodek, bois d’arc, hedge osage, horse apple, mock orange, wild orange, etc.

          The Jerusalem cherry is a woody plant about 1’ tall, its fruit is a berry, not a cherry, and it doesn’t come from Jerusalem. Likewise the Jerusalem artichoke is neither an artichoke, nor does it come from Jerusalem.

          In Europe with its many languages, common names can become very numerous. The cosmopolitan weed, Plantago major, for example, is often called broad-leaved plantain in English, but it also has ca. 45 other names in English, 11 names in French, 75 Dutch names, and ca. 106 names in German. Had it not been for the early recognition by biologists and others for the need for worldwide uniformity in naming and classifying all organisms, utter chaos eventually might have prevailed in communications concerning them.


Common names for plants do not indicate any relationship with other plants; there is no hierarchy of classification, and therefore no predictive value, and evolutionary relationship implied by the name.


More curious common names

1.     pineapple – neither a pine nor an apple

2.     peppergrass – not a pepper, nor a member of the grass family

3.     The logic behind names such as “ramping fumitory”, “bastard toadflax”, or “bouncing bet” is not very apparent.

4.     Kentucky bluegrass was introduced from Europe, and California pepper tree from Peru.


Some scientific names are worth pondering as well:

1.     Viola purpurea is yellow flowered, not purple as the specific epithet implies.

2.     Unifolium bifolium – okay, is it one-leaved or two?


Some names of local plants:

1.     Acacia greggii is also known as catclaw or “wait-a-minute-bush”

2.     Peucephyllum schottii is known as desert fir, and its dark green leaves resemble the needles of firs

3.     Petalonyx thurberi, known as sandpaper plant, is readily apparent when you rub the leaves of the shrub.

4.     Larrea tridentata – creosote, referring to the olfactory similarity to the pungent wood preservative used on fence posts and telephone poles.

5.     Hymenoclea salsola, cheese-bush, smell like cheese.

6.     Malva parviflora, cheese-weed, produces wheel-shaped fruits composed of one-seeded sections.