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TAXONOMY OF VASCULAR PLANTS: Part One

04.1 Categories of classification

categories.htm

by George H. M. Lawrence, Professor of Botany at the Bailey Hortorium, Cornell University, 1951

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Contents of this page

Principles of Taxonomy
Major categories of classification
What is a family?
    Phylum > Subphylum > Class > Order > Family > Genus
    Name-endings: -eae / -ale / -ineae / - aceae / -oideae / -inae
Minor categories of classification
What is a genus?
What is a species?
Infraspecific categories
What is a subspecies?

Foot notes

UKT notes
carpel class ecotype forma
genus germ-plasm order
phylum pistil
taxon tribe

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04. Principles of Taxonomy

[{p042}]

Taxonomy is a functional science. The direction, character, and extent of its functions are guided by principles that have developed with the increase in knowledge of the plants themselves. [UKT ]

The formulation of these principles began with the period of descriptive taxonomy which functioned on a scientific level in the nineteenth century, and only recently has waned and may become secondary in importance. This descriptive period began with the works of Tournefort, de Jessieu, and Linnaeus. Most taxonomic work of the period was based on observations of the similarities and differences of usually gross morphological characters of the plants concerned. [UKT ]

Plants were described and classified on the basis of these characters. The describing of plants from newly explored areas was then a major function of taxonomy. Succeeding these pioneers were such leaders as Robert Brown, the Hookers (William and his son Joseph), John Lindley, and George Bentham, all of England; the three generations of de Candolles of Geneva and Paris, Edmund Boissier of Geneva, Carl Willdenow and Curt von Sprengel of Berlin, Eduard von Regel of Leningrad, and Asa Gray of Cambridge (Mass.).

During this period these and other systematists published various principles of taxonomic procedure. The first of these was by Linnaeus in his Critica botanica (fn042-01).1 Other were by Adanson, John Lindley, de Candolle, and Sir Joseph Hooker. [UKT ]

Many of the criteria established by these early botanists have withstood the test of time and are accepted by contemporary workers. More important, however, is the recognition by present day taxonomists that gross morphological characters are not always adequate to provide reliable means of differentiation between features that are of major significance from those of minor significance, or to serve necessarily in the determination of genetical relationships between taxa. This recognition has resulted in the need for a re-evaluation of all taxonomic work conducted by these earlier devotees of the descriptive [{p043}] method, a re-evaluation that will take into consideration, in addition to the morphological criteria, all other scientific data pertinent to the situation and as contributed by allied botanical sciences. [UKT ]

Present-day taxonomy is based on the primary importance of morphological distinctness and affinity, but it is influenced appreciably by the findings of the cytologist, geneticist, anatomist, and others.

The principles of taxonomy are concerned primarily with the criteria employed. However, the intelligent discussion of these criteria presupposes an understanding of the units of classification. For this reason it is appropriate that an explanation and discussion of the latter precede other objectives of this chapter.

Taxonomy is based on the hypothesis that genetical relationships exist between plants, that present-day plants are, through successive generations, the offspring of ancestral plants that may or may not now be extant. It is based also on the assumption that there has occurred, during the developmental epochs of the earth's history, an evolution of plant characteristics to the extent that surviving plants often were of increased structural complexity and genetic organization over their ancestors. [UKT ]

As these evolutionary processes progressed, the much-removed offspring of ancestors that one were extant and were closely related have become less closely related -- to the degree that today the determination of plant relationships is almost wholly a subject based on postulations, hypotheses, and tenuous conjectures. Because of the predication of the science of taxonomy on these concepts of genetic relationship, it is desirable to place plants in categories that are indicative of their presumed genetic affinities. [UKT ]

Each category represents a group of plants; as species, genera, families, etc. No one of these is subject to precise definition, their delimitation or circumscription varies, and each is subjective in character (fn043-02). [UKT ]

Groups such as Angiospermae, Monocotyledoneae, or Rosales are of considerable magnitude. They are, respectively, examples of the categories of subdivision, class, and order. Each of these is composed of many and diverse kinds of plants, and although each is an example drawn from a different level of classification, collectively they many be referred to as major categories. The more familiar groups, represented by such examples as Petunia (a genus), regal lily (a species), or cabbage (a variety) are of relatively small magnitude and by comparison are of minor categories. [UKT ]

A minor category may be considered one whose name is also a part of the name of the particular plant. A major category is [{p044}] any one of the higher categories whose names are not a part of the name of the plants belonging to them. [UKT ]

The major categories of vascular plants have been reasonably well established in recent decades and their circumscriptions are the special studies of the phylogenist rather than of the ordinary taxonomic worker. The minor categories have been the subject of more intense study by a greater assemblage of workers and for this reason have been interpreted more diversely. Each of the more important categories is discussed below individually, with those of major magnitude preceding those of narrower limits.

The categories of taxonomic groups and the terms denoting them are prescribed by Chapter II of the International Rules of Botanical Nomenclature (ed. 3), of which Article 13 states:

The definition of each of these categories varies, up to a certain point, according to individual opinion and the state of the science; but their relative order, sanctioned by custom, must not be altered. No classification is admissible which contains such alterations.

To the extent that the above-quoted article applies, the subject of classification units is one of nomenclature. The definition and general circumscription of the categories is a subject of classification and is a vital part of the principles of taxonomy.

UKT: As an example of how a plant species is classified, below is the classification of India mustard (from: USDA-NRCS)

Kingdom -- Plantae Plants
Subkingdom -- Tracheobionta Vascular plants
  Superdivision -- Spermatophyta Seed plants
  Division (aka phylum) -- Magnoliophyta Flowering plants
    Class -- Magnoliopsida Dicotyledons
    Subclass -- Dilleniidae
      Order -- Capparales
        Family -- Brassicaceae Mustard family
          Genus -- Brassica L. mustard
          Species -- Brassica juncea (L.) Czern. India mustard

Details of the classification terms are discussed below.

 

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Major categories of classification

In biology, a phylum (pl. phyla) is a taxonomic rank below kingdom and above class. Traditionally, in botany the term "division" is used instead of "phylum", although in 1993 the International Botanical Congress accepted the designation "phylum". The Animal kingdom contains approximately 35 phyla; the Plant kingdom contains 12 phyla. -- from Wikipedia: http://en.wikipedia.org/wiki/Phylum 121228
Based on the above I have changes between division and phyla in this section. -- UKT 121228

The plant kingdom is divided into phyla. Zoologists divide the animal kingdom into phyla, and for purposes of conformity of category names between the two branches, some biologists and botanists have adopted for plants the term phyla [sing. phylum] in place of division. The term division (phylum) is prescribed by the rules of nomenclature to represent the category of highest magnitude within the plant kingdom, whereas phyla is not mentioned. [UKT ]

The number of phyla into which the plant kingdom is divided varies with different systems of classification. By some authors it was considered to be four; by the latest revision the widely current Engler system it was considered to be 12. [UKT ]

Among vascular plants the Spermatophyta (seed plants) may represent a phylum ( fn044-03). It is not possible to define a phylum concisely or with precision. Phyla of vascular plants are relatively few in number. They are taxa that are distinguished by characters that are common only to the constituent elements of each phylum. For example, the Spermatophyta are characterized, in part, by the possession of a sporophyte generation that is dominant over the much [{p045}] reduced gametophyte generation, by the presence of ovules, and by the production of reproductive structure called seeds. [UKT ]

The characters employed are often of reproductive, morphological, or internal anatomical structures. For the most part, it is true that these selected characters are believed to have been fundamental to early ancestors and that their presence throughout an extended sequence of generations undoubtedly was responsible in part for survival of present-day representatives. It must be recognized also, these are biological material and all possessing the germ-plasm that is life, that in the far distant past, the components of one phylum had one or more ancestors in common with the components of another phylum. [UKT ]

The existence of these relationships means that the boundaries or criteria by which one phylum is separated from another phylum are not so sharp, clear-cut, or inviolate of exception as one may be led too believe. Exceptions do exist and may be observed for almost every divisional (phylum) character. For this reason the phylum is characterized by and aggregate of characters rather than by any single infallible one. Similar situations exist in all major categories of plants.

It is provided by the rules of nomenclature that any category of plants may be divided into subordinate categories intermediate between it and that of next lower rank. This is accomplished by adding the prefix sub to the name of the higher category. [UKT ]

By this provision, a phylum may be composed of two or more subdivisions (subphyla), or (when the intermediate category is not required) a division (phylum) may be composed of two or more classes. The phylum Spermatophyta was divided into two subdivisions (subphyla), the Gymnospermae and the Angiospermae. On the other hand, the phylum Pteridophyta was subdivided, not into subphyla, but directly into categories called classes. The is because fewer kinds of categories are recognized within the Pteridophyta than within the Spermatophyta.

A phylum or subphylum is composed of classes. The class is the next full category subordinate in rank to the division (phylum). The names applied to classes are Latin names, as are those of all taxonomic categories, and ordinarily have the ending -eae. [UKT ]

The two classes of the subphylum Angiospermae are the Monocotyledoneae and Dicotyledoneae. The Gymnospermae are not subdivided into classes by most authors, but are treated as composed of a number of distinct orders, a category explained below. In the case of the Dicotyledoneae the number of kinds of plants is so great that most phylogenists have treated them as composed of several subclasses. There has been no accord in the selection of names applied to these subclasses or in the selection of taxonomic bases on which they have established. [{p046}]

Each class (or subclass, when present) is subdivided into orders. The order is the category next in line and subordinate to that of class.4 ( fn046-04) The Latin names of orders conventionally have the ending -ales, as Rosales or Cycadales. However, the names of some orders of long standing, and which were given to the taxa before the existence of currently accepted rules of nomenclature, do not terminate in -ales but rather have the ending -ae. These names have priority and nomenclaturally are allowed. Examples of them are found in the names Glumiflorae and Tubiflorae (the orders to which belong respectively the grasses and asters). [UKT ]

An order possesses a degree of phylogenetic unity that is determinable with greater assurance than that of the higher taxa of division or class. The relationships of its components and their eligibility for inclusion within the category can be ascertained by and established on more definite criteria and characteristics.

In some cases it has been found desirable to treat large orders as comprised of suborders. It is customary, and in accordance with the rules, to terminate the names of these suborders with the ending -ineae as Malvineae, a suborder of the Malvales.

An order of plants is comprised of one or more families. The category of family is the smallest of the major categories and, of them, is the most frequently encountered in ordinary taxonomic studies. The Latin names of all but 8 of the families of vascular plants are terminated by the conventional ending -aceae, as Pinaeeae, Rosaceae, or Ranuneulaceae. Certain family names sanctioned by long usage do not end in -aceae and have irregular terminations that are allowed as exceptions to the rule. These families are: Palmae, Gramineae, Cruciferae, Leguminosae, Guttiferae, Umbelliferae, Labiatae, and Compositae. However, the Rules (ed. 3) authorize the substitution of an alternative name ending in -aceae, as Poaceae for Gramineae.

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What is a family?

A chemist working with Medicinal Plants, needs to know the family, the genus, and the species of a plant. For checking the plants he is getting for his work, he needs to know what it looks like, the odour, and taste of the parts. -- UKT121229

The family usually represents a more natural unit than any of the higher categories. This is true because usually more is known about the components of a family, and correlations between a greater number of characters usually exist. For example, families such as the grass family, the sedge family, the mustard family, and innumerable others, are readily recognized as natural taxa whose respective members have definite characters bonding them together. [UKT ]

Not all families, or taxa conservatively [{p047}] recognized as such by many botanists, are natural. Examples of such unnaturalness are to be found, among flowering plants, in the Englerian concept of the Saxifragaceae and Onagraceae and, in the ferns, in the conservative concept of the Polypodiaceae. Each of these families is an unnatural taxon and, as currently and conservatively broadly delimited, must have been derived from heterogeneous and relatively unrelated ancestors; that is, they are presumed to be of polyphyletic origins. The solution to the problems presumed by these unnatural families may rest in their division into smaller phylogenetically homogeneous families. [UKT ]

UKT: In the above para, we are meeting the technical term "taxon" (pl. taxa) for the first time. See my note on taxon and also footnote fn053-08 .

The natural family is believed to be one whose members were derived from common ancestral stock (i.e., of monophyletic origin). The families of higher plants are separated from one another by characters generally inherent in the reproductive structures. They are characters usually associable with features such as inflorescence type, ovary position, placentation type, pistil and carpel number, ovule type, embryology, such androecial conditions as monandry, diandry, and syngenesism, and the disposition of sexes as in dioecism and monoecism. [UKT ]

The increase in knowledge of the origins, interrelationships, and ancestral types of these features will gradually result in the resolution of many of the problems concerned with the more accurate determination of family circumscription. A family is not of any particular size; it may be comprised of one genus or of 100 genera. Its claim to this rank lies with the degree and constancy by which it differs from other families within the same order or suborder.

When a family is large and comprised of many components, it is often found desirable to divide it into phyletic units called subfamilies. These bear Latin names that usually are terminated by the ending -oideae. One subfamily of the Rosaceae is the Rosoideae, another of the same family is the Pomoideae. [UKT ]

Large subfamilies are sometimes subdivided into tribes, which are subordinate phyletic groups whose Latin names have the ending -eae. One tribe of the Compositae is the Astereae, another the Inuleae. In some cases a family is divided directly into tribes. Occasionally it is desired to recognize phyletic groups subordinate to the tribe; these are called subtribes. They are designated by Latin names ending in -inae.

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Minor categories of classification

A minor category of classification is considered here to be one whose name becomes a part of the name of the plant. It may be a genus, a species, or any one of the several categories subordinate in rank to the [{p048}] species. [UKT ]

For reasons of phyletic clarity and convenience in classification, the category of genus is sometimes subdivided into subgenera, sections, subsections, and series. These latter are  phyletic  groups whose Latinized names do not enter into the name of the plants concerned and which basically are not of the same functional significance as is the category of genus, species, or variety. [UKT ]

As mentioned at the beginning of this chapter, more workers are concerned with the minor categories of classification than are concerned with the major ones. Because of this, more data are available concerning the components of these units, and more diversity of opinion and concept exists concerning their delimitations. [UKT ]

In general, the concepts of these minor units are represented by two or more schools of thought, and it is desirable to present the views of these as objectively as possible. For details other than those provided below the student is as possible. For details other than those provided below the student is referred to articles cited in the bibliographic references at the close of this chapter.

The genus is subordinate to family. Each family is comprised of one or more genera. The generic name of plant is the first of the two words comprising a binomial as, for example, in the binomial Quercus alba the generic name is Quercus. The Latin names of genera are substantives (or adjectives used as much ), are always capitalized, are always in the singular number, and may be taken from any source whatsoever or composed in an entirely arbitrary manner. They have no uniform endings.

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What is a Genus?

The genus is a category of long standing. It is highly probable that genera were recognized as groups of plants of common affinity before science came of age, and before written languages existed. [UKT ]

Among the early herbalists, Oscar Brunfels (UKT: related to Otto Brunfels?) is credited with having had the clearest concept of the category of genus. [UKT ]

UKT: See my note on Ancient Herbals

A little over a century later, in 1716, there was published (posthumously) a monumental work by the French botanist Joseph Pitton Tournefort, Institutiones rei herbariae, wherein he developed his thesis that the fundamental category of classification was the genus, and that plants having in common two or three characters of reproductive structures were usually to be treated as members of the same genus. Basically the Linnaean concept of the genus (1737 et seq.) was in accord with that of Tournefort, and in this respect it is significant that of our common indigenous plants, more of them are in genera named and circumscribed by these two men than have been named subsequently by other botanists.

Any consideration of the concepts of the generic category must recognize that the philosophies of these early and great men were of a period when the theory of Special Creation prevailed, a doctrine accompanied [{p049}] by the corollary that life forms were immutable. [UKT ]

It was during this period of dogmatism that basic tenets were established by which much of our currently available taxonomic literature was written. This literature was based on a system ''organized on a basis of similarities, having as its fundamental principle a doctrine based on the thesis that a community of similar morphological structures indicates relationship" (Camp, 1940, p.382). [UKT ]

The genera of Linnaeus, Rafinesque, Hooker, Gray, Torrey, and of later botanists were based largely on the belief that a genus is a category whose components (i.e., species) have more characters in common with each other than they do with the components of other genera within the same family. This concept of the genus is supported by many contemporary taxonomists. [UKT ]

An inherent weakness of this concept is that in circumscribing genera, often within a given family, it is not possible to treat selected characters as possessing equal value for all genera of the same family. It very often happens that characters that are adequate to separate some genera within a family are insufficiently stable to separate even species within another genus of the same family. Despite this shortcoming, the concept has provided an expedient solution to practical need: it has served and will continue to serve a purpose.

Many botanists  believe that the genus is more than a taxonomic category. If the theory of evolutionary descent via the transfer of mutable germ-plasm through successive generations is accepted, then just as it is the goal that taxa represented by the higher categories be arranged within a natural and phyletic system of classification indicative of genetic relationships, so also is it desirable that the category of genus be treated as a phyletic unit; a category circumscribed and disposed to indicate the phyletic relationships of it and its components with other similarly established genera and their components. [UKT ]

This second concept treats the genus as a biological category, and taxonomic studies of genera that accept this concept take into account not merely the morphological similarities by which it is conventionally recognized, but also the origins, migrations, genetic, cytologic, physiologic, and ecologic behavior, and geologic history associated with its components. [UKT ]

The re-evaluation of existing genera by the tenets of such a concept must result in some genera being divided into segregates, other being combined with what were thought to have been distinct genera, and still others maintaining their status quo. Genera established by adherents of the first concept are the products of descriptive taxonomy, whereas those redefined according to the second concept are the products of a modern phyletic taxonomy.5 ( fn049-05) [{p050}]

A genus may be divided into subgenera and they in turn into sections, subsections, and series, or the genus may be treated as composed of sections without the intercalation of subgenera. Some genera are not subdivided, but comprise only a group of very homogeneous species. The names of generic subdivisions are usually adjectives in the plural number and agree in gender with the generic name.

The species long has been considered to be the basic unit of all taxonomic work. [UKT ]

This view had its origins in earliest civilizations and the species was the category on which the theory of Special Creation founded its beliefs (note that Homo sapiens is a species). This theory postulated that all the kinds (i.e., species) of plants and animals were created in their present form, that the number of species then on earth was the same number that had been there since the beginning of time, and that having these species man proceeded to devise classifications whereby they were grouped into  genera, the genera into families, the families into orders, and so on. [UKT ]

According to the theory of evolutionary development, no single category is a basic phyletic unit, for the category of species is no more fundamental to a phylogenetic schema than is any other category, and all categories must be accepted as somewhat artificial and all considered as interlocking links in a 3-dimensional composite of relationships. However, despite this, it must be recognized that nomenclaturally the species is the category on which the binomial system has been established. It is the category that has received more attention by biologists than all others combined.

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What is a species?

UKT: Charles Darwin published his book titled "On the Origin of the Species" on 24 November 1859. -- http://en.wikipedia.org/wiki/On_the_Origin_of_Species   121231. The book was written for non-specialist readers and attracted widespread interest upon its publication. Yet, do I, as a professed Theravada Buddhist, and a material scientist, specifically, know what a "Species" is? -- UKT 121231

Botanists of every generation have attempted to answer this question, one for which there may be no single answer. An approach to an answer was provided by Camp and Gilly (1943-pp.380-318), who wrote that:

There are even some among us who have advocated that we discard the concept of a species altogether. Therefore, the question which the systematist should seek first to answer is not: Upon what criteria should the concept of a species-unit be based? Rather, he must enquire: Does the species-unit deserve to be a fundamental philosophical concept? This, perhaps fortunately for his own peace of mind, has long ago been decided for him.

The concept of species or kind, as a unit, has become so firmly entrenched in the mind of man -- so much a part of his awareness, so necessary to his basic philosophy -- that it remains only for the systematist to interpret  this unit . . .

There are many schools of thought that have attempted to produce interpretations of the unit, but the number of botanists holding to different views is diminishing. The time honored answer to the question of "What is a species?" has been that a species is a concept, that it is the [{p051}] product of each individual's judgment. [UKT ]

The modern taxonomist requires more data in the jelling of a species concept for, in addition to morphological distinctions, inquiry is made of the character and extent of morphological variation within the populations that collectively are treated as a species; to these may be added considerations of distribution that may or may not take into account the geologic history of the areas concerned. [UKT ]

This concept was undoubtedly of major importance to du Rietz (1930), who postulated that species were "the smallest natural populations permanently separated from each other by a distinct discontinuity in the series of biotypes." [UKT ]

This view stresses the importance of morphological continuity transmissible from one generation of components of the species to another. Lamprecht (1949), a cytogeneticist, traced the developments of and changes in species concepts, classifying them to be identified with one of the following five periods of taxonomic research:

"1. descriptions without taxonomic systems.
 2. the period of development of artificial and natural systems,
 3. systems in the light of evolution,
 4. the period beginning with the detection of speciation by addition of genomes, and
 5. that beginning with the detection of the genic basis of the species barrier."

From this view it is clear that most current taxonomic work comes within his third period, and that the biosystematist is now working in the last two periods.

Any consideration of solutions to the species problem must take into account the current views that

(1) all populations tend to vary and that no two are ever exactly alike,
(2) that some of these variations are adaptive and are of survival value,
(3) that forces of nature result in the extinction of some individuals while others survive the same forces,
(4) that some of the variations displayed by individuals within a population must be hereditary if successive generations are to be modified from ancestral conditions, and
(5) that the environment of the individuals must not be static lest the course of evolution by checked by the forces of natural selection.

These views collectively incorporate the principles of the theories of natural selection and of evolution. If they are pertinent to the background and evolution of the individual and likewise through aggregates of individuals, of the species, it is apparent that there must be many kinds of species. These kinds of species are biologically different taxa that have arisen by means of different selective and genetic mechanisms.6 (fn051-06) The species is perpetuated by one of a relatively few types of reproduction. [UKT ]

Sexual reproduction plays the dominant role, but within [{p052}] this type of reproduction the "fertility relations between the individuals or between intraspecific groups will certainly affect the type of the population" (Babcock, 1947,I,35). In addition to these, the genetic constitutions of populations vary, for as shown by chromosome complements, the plants may be diploids, or they may be various kinds of polyploids. [UKT ]

Plants of different genetic constitution behave differently, the progeny may or may not be like their parents, and by virtue of the potentials inherent in these internal genetic conditions, plants may be sexually compatible or incompatible migrate or regress, or may survive or perish. [UKT ]

It has only recently been recognized that asexual reproduction also may be responsible for kinds of species. It has become established that certain populations often treated as species do not reproduce sexually but rather by asexual devices, many of which are obscure and superficially not apparent. This may be accomplished by various types of apomixis such as parthenogenesis or simple vegetative reproduction of clonal elements.7 (fn052-07) These different kinds of species may be differentiated. The recognition by Clausen, Keek, and Hiesey (1939) of the significance of these genetic factors in the speciation of plants resulted in a subclassification of species which has gained considerable support and is presented in detail in Chapter 8.

From this it is apparent that the problem of speciation is not simple. The taxonomist is faced with the need of acknowledging that biologically there are different kinds of species and that each species represents a kind of population. Accompanying this is the recognition that these genetic systems called species must be resolvable into the existing functional binomial system of nomenclature.

The existence of different and sometimes seemingly divergent views on the subject of what is a species need not be confusing. It is important to know that they exit. It is desirable of them so that they may be rationalized and evaluated. [UKT ]

In arriving at an opinion, it should be remembered that in most instances there are yet insufficient data by which to determine the speciation status by the standards of the biosystematist, and that for purposes of expediency and practicality the taxonomist must give to the populations under study

" (1) a circumscription which is not only biologically as sound as possible, but
  (2) which also is in accord with an effective system of nomenclature.

Furthermore, the interpretation of these [{p053}] items must be balanced; there must be no undue emphasis on one above the other, otherwise a bifurcation of concept will result leading to chaos in systematics." (Camp and Gilly, 1943,p.381).

Irrespective of the nature of the concept by which species are circumscribed, the unit must fit into the binomial system of nomenclature. It must have a Latin name and that Latin name composed of two words -- the generic name and the specific name -- is the binomial governing the subject of binary names are presented in Chapter 9.

In addition to the terms applied to these major and minor categories, there has been proposed the term taxon (plural, taxa) as being more adequate and specific than such ambiguous terms as entity or taxonomic group .8 (fn053-08) [UKT ]

The term entity is unsatisfactory since no taxonomic or biologic category above that of the individual can strictly be an entity, and the term group is inadequate since it is a collective term not properly applicable to an individual plant. The term taxon has the merit of possessing a single meaning, unfettered by vagueness or ambiguity. It is short yet descriptive. It is believed that its acceptance will add clarity and precision to biological literature.

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Infraspecific categories

Any category below the rank of species is an infraspecific category. It is a variant of the species.9 (fn053-09) [UKT ]

Taxonomically, the origin of species variants has been the subject of two basic philosophies. [UKT ]

According to the first, botanists of the nineteenth century and earlier consistently in their taxonomic works would establish a species. Then if it was determined that a variant of that species existed, the variant was named and described as if  it were an appendage to the species. This philosophy [{p054}] stemmed directly from the Theory of Special Creation, for the variant was not considered to be a genetic part of the species, but rather was an orphan element apart by itself that did not merit species rank but was attached to that species which it most closely resembled. Such was the philosophy of men from the time of Linnaeus to Asa Gray and later. [UKT ]

Full comprehension of the dynamic forces inherent in the theories of evolution resulted in the second and more recent philosophy that biologically a species comprises the element represented by the initial binomial and all subsequently described variants ascribed to that binomial. [UKT ]

In other words, by this later philosophy, it was merely by chance that one plant (or population) served to be the basis (nomenclatural type) of the new binomial (i.e., species). If it had happened that one of the elements later treated taxonomically and nomenclaturally as a variant of a binomial had been discovered first, then the second element would have been the typical element of the species (i.e., it would have been the initial element first to have been designated by a binomial) and the first would have become a variant of it. That is, if the variant and the typical element of a species are of the same rank they are presumed to be biological equivalents, one is no more the species than is the other. [UKT ]

Properly speaking in technical treatments, the description of the species as represented by the binomial would then be of a scope that would account for the characteristics of all varietal elements of it and not of the typical element alone. If the species is thus broadly circumscribed, the typical element is to be contrasted with successively described variants and treated nomenclaturally in a definite category subordinate to the species and coordinate with other included elements of the same infraspecific rank. When more than one infraspecific taxon is present, a trinomial form of nomenclature is followed, as, for example, Carex aquatilis var. aquatilis for the typical element, and Carex aquatilis var.altior for infraspecific taxon of it.

The rules of nomenclature provide for the infraspecific categories of subspecies, varietas, subvarietas, forma, forma biologica, forma specialis, subspecies, variety (varietas), and forma. [UKT ]

The situation exists here, as it does with respect to the category of species, that there are differences of opinion as to what is a subspecies, a variety, or a forma.

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What is a subspecies? 

The subspecies has been given many definitions, but of them the following may serve to indicate the basic differences of concept :

1. that they are baby species or species of small magnitude that are distinguished by less obvious or less significant morphological features than are more [{p055}] obvious species within the same genus;

2. that they are major morphological variations of a species that have geographic distributions of their own, which are distinct from the area occupied by other subspecies of the same species; or,

3. that a subspecies is the category to which should be referred those elements which by possession of satisfactory geographic, ecologic, and morphologic characters are suspected to be counterparts of the ecotype (a biologically significant element determinable only after analysis by slow and tedious experimental techniques). 10 ( fn055-10)

The use of the category subspecies is receiving increasing favor by taxonomists, but in each case it must be determined which of the three basic types of concept was adopted by the author. For example, the subspecies of the Englerian school was a category of major morphological distinction with or without disjunctive distribution. By earlier European botanists (Link, Sprengel, et al.) it was reserved for horticultural elements, by early devotees of the American Code it was "applied indiscriminately to anything below the rank of species" (Weatherby, p. 161), and by some contemporary biosystematists it is employed for an unproved but suspected ecotype. (For definition and discussion of the term ecotype, cf. pp. 176-177.)

The variety (Latin, varietas) has been used as a category to designate as many or more concepts as has that of subspecies. Horticulturists have used it indiscriminately for any variant of the species; botanists have considered it to be :

(1) a morphological variant of the species without regard for distribution,
(2) a morphological variant having its own geographical distribution,
(3) a morphological variant sharing an area in common with one or more other varieties of the same species, and
(4) a variant representing only a color or habit phase. From this it is clear that the same plant may be designated a subspecies by one botanist and a variety by another or that the variety of one author is placed in the category of forma by another author. [UKT ]

This lack of unanimity of concept is disconcerting, but it is a factor to be recognized in any appraisal of taxonomic literature. In this regard, it is not especially important that agreement exist if by even diverse modes of evaluation the same pattern of relationship is reached. There is no historical basis for priority of usage of either the term subspecies or variety. As stated by Fosberg (1942),

The solution seems actually simple enough, if one recognizes that there are many types of evolutionary process in operation, producing many kinds of species, and [{p056}] that intraspecific units may be incipient species in various stages of development. These stages may be at least roughly indicated by the categories in which the groups are placed. [UKT ]

Each taxonomist may take up the system of categories set up in the International Rules and apply it to the groups of plants with he is working in the way that, in his judgment, best expresses the relationships of the groups of individuals concerned. The Rules require only that the order of the categories be not disturbed, and that each plant be placed in a species, genus, family, order, class, division and kingdom. All other categories are to be used at the discretion of the worker. In this way the system will retain the flexibility that is absolutely essential to make it fit the wide variety of evolutionary situations to which it must apply. Discarding any of the categories, whether from reasons of historical confusion or personal prejudice, impairs this flexibility.

The forma is commonly the smallest category used in ordinary taxonomic works. It is generally applied to trivial variations occurring among individuals of any population. Such variations as represented in corolla color, fruit color, habitat response are, by this concept, placed in the category of forma. Some botanists consider a forma to be any variant that occurs sporadically in a species population irrespective of the degree of morphological variation or constancy, the significant criteria being that of no geographical discontinuity. The forma of this latter concept is equivalent to the variety of many botanists.

Lesser categories below that of forma appear in the literature, primarily in European floras and in horticultural works. The category termed a race is employed in some floras in lieu of or subordinate to the term forma.11 ( fn056-11). In horticultural work, the term clone12 ( fn056-12) is applied universally to individual plants that are propagated by asexual (vegetative) means. The original definition of the term inadvertently has been considerably amplified and emended by some geneticists and biosystematists to include also those indigenous plants that reproduce asexually by apomixis.

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Footnotes

fn042-01. For the latest English translation from the Latin, see that by Sir Arthur Hort.
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fn043-02. For a historical account of the development of higher categories of classification and considerations of the diversified nomenclature given them, see Croizat (1945) and Just (1945).
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fn044-03. By the Engler system, this division (phylum) bears the less familiar name, Embryophyta Siphonogama.
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fn046-04. Earlier botanists employed the them order for the category now named family. This former interpretation was used in the Bentham and Hooker system of classification and is encountered in some current floras based on this system. The International Rules of Nomenclature (ed.3) prescribe its use as indicated above and make its use illegitimate in lien of the term family.
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fn049-05 . For discussion of the delimitations of genera, see Moran (1942)
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fn051-06. For discussions of the kinds of species and their genetic origins, organizations, and behaviors, see Camp and Gilly (1943) and Lamprecht (1949).
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fn052-07. For an analytical review of literature on the role of apomixis in species formation, see Chapter VIII, pp, 184- 185, and Stebbins (1941), and Gustafsson (1946-47)
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fn053-08. The term taxon was presented at Utrecht symposium on nomenclature, convening during the summer of 1948, by H. J. Lam, who formally proposed "to indicate  taxonomic groups of any rank with the term  taxon (plural: taxon). This term was first introduced by A. Meyer in his : Logik der Morphologic im Rahmen einer Logik der gesamten Biologic, 1926,p. 127;cf, also pp. 133, 241." It is believed that Meyer did not mean to introduced the term taxon to be used for any systematic unit. He introduced it to distinguish a minor category in taxonomy from a major category of phylogeny that Haeckel (in Generelle Morphologie 1:2 1866) had designated phylon. At the International Botanical Congress, held in Stockholm, 1950, it was voted to used the term taxon throughout the next edition of the Rules of Botanical Nomenclature, wherever appropriate.
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fn053-09. The designation infraspecific category is introduced to avoid the ambiguity occasioned by the use of subspecific category, since an infraspecific category clearly is any of several categories subordinate to that of species, whereas a subspecific category may be used in this sense or may be used more strictly to designate the category of subspecies.
   The term variant is used here in the literal sense; for any element differing from the typical, and is not to be confused with the term variety; the latter being an English translation of the Latin Varietas, a technical term used to designate a particular category subordinate to the rank of species. 
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fn055-10. For details concerning these and other concepts of the subspecies category, cf. references in bibliography to papers by R. T. Clausen, Du Rietz, Fernald, Fosberg, Pennell, Weatherby.
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fn056-11. By some authors of biosystematic works the race or ecological race is used in lieu of the term ecotype. This usage may be unfortunate and seemingly may add to the ambiguities of terminology, since the term ecotype (although of varying definition) is now well established in the literature and need not be abandoned for etymological reasons nor simplified to facilitate understanding. The term race has been used in other senses by geneticists and its use as a taxonomic category by some European systematists is not to be ignored.
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fn056-12. For discussions of the origin and spelling of the term and its application, see Stearn, W. T. (1947)
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UKT notes

carpel

carpel n. 1. One of the structural units of a pistil, representing a modified, ovule-bearing leaf. [New Latin carpellum from Greek karpos fruit; See kerp- in Indo-European Roots.] -- AHTD

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class (Biology)

class n. 5. Biology A taxonomic category ranking below a phylum or division and above an order. See note at taxonomy . -- AHTD

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Ecotype

From Wikipedia: http://en.wikipedia.org/wiki/Ecotype 1212301

In evolutionary ecology, an ecotype, [note 1] sometimes called ecospecies, describes a genetically distinct geographic variety, population or race within species (or among closely related), which is adapted to specific environmental conditions. Typically, ecotypes exhibit phenotypic differences (such as in morphology or physiology) stemming from environmental heterogeneity and are capable of interbreeding with other geographically adjacent ecotypes without loss of fertility or vigor. [1] [2] [3] [4] [5]

Example

Tundra reindeer and forest (or woodland) reindeer are two ecotypes of reindeer. The first migrate (travelling 5,000 km) annually between the two environments in large numbers whereas the other (who are much fewer) remain in the forest for the summer. [7] Currently, and since 1961 classification, tundra reindeer comprise five subspecies and woodland reindeer two. [8]

UKT: More in the Wikipedia article

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forma

From Wikipedia: http://en.wikipedia.org/wiki/Form_botany 121231

In botanical nomenclature, a form (forma, plural formae) is one of the "secondary" taxonomic ranks, below that of variety, which in turn is below that of species; it is an infraspecific taxon. If more than three ranks are listed in describing a taxon, the "classification" is being specified, but only three parts make up the "name" of the taxon: a genus name, a specific epithet, and an infraspecific epithet.

The abbreviation "f." or the full "forma" should be put before the infraspecific epithet to indicate the rank., e.g. Acanthocalycium spiniflorum f. klimpelianum  . 

UKT: More in the Wikipedia article.

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genus

From Wikipedia: http://en.wikipedia.org/wiki/Genus 121229

In biology, a genus (plural: genera) is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia. Genera and higher taxonomic levels such as families are used in biodiversity studies, particularly in fossil studies since species cannot always be confidently identified and genera and families typically have longer stratigraphic ranges than species. [1]

The term comes from Latin genus "descent, family, type, gender", [2] cognate with Greek: γένος genos, "race, stock, kin". [3]

The composition of a genus is determined by a taxonomist. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. In the hierarchy of the binomial classification system, genus comes above species and below family.

The scientific name of a genus may be called the generic name or generic epithet: it is always capitalized. It plays a pivotal role in binomial nomenclature, the system of biological nomenclature.

UKT: More in the Wikipedia article

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germ-plasm

From Wikipedia: http://en.wikipedia.org/wiki/Germ_plasm 121229
UKT: For ease of understanding I have hyphenated the words, "germ-plasm", "egg-cells", "germ-cells".

Germ-plasm or polar plasm is a zone found in the cytoplasm of the egg-cells of some model organisms (such as Caenorhabditis elegans, Drosophila melanogaster, Xenopus laevis), which contains determinants that will give rise to the germ-cell lineage. As the zygote undergoes mitotic divisions the germ-plasm is ultimately restricted to a few cells of the embryo. These germ cells then migrate to the gonads.

Germ-plasm theory

The term germ-plasm was first used by the German biologist August Weismann (18341914). His germ-plasm theory states that multicellular organisms consist of germ cells that contain and transmit heritable information, and somatic cells which carry out ordinary bodily functions. [1] [UKT ]

In the germ-plasm theory, inheritance in a multicellular organism only takes place by means of the germ cells: the gametes, such as egg-cells and sperm-cells. Other cells of the body do not function as agents of heredity. [UKT ]

The effect is one-way: germ-cells produce somatic-cells, and more germ-cells; the germ-cells are not affected by anything the somatic-cells learn or any ability the body acquires during its life. Genetic information cannot pass from soma to germ-plasm and on to the next generation. This is referred to as the Weismann barrier. [2] This idea, if true, rules out the inheritance of acquired characteristics as proposed by Jean-Baptiste Lamarck. [3]

The part of Weismann's theory which proved most vulnerable was his notion that the germ-plasm (effectively, genes) were successively reduced during division of somatic cells. As modern genetics developed, it became clear that this idea was quite wrong. [4] [UKT ]

Cases such as Dolly (the famous cloned ewe) which, via somatic cell nuclear transfer, proved that adult cells retain a complete set of information as opposed to Weismann's increasingly determined gradual loss of genetic information putting this aspect of Weismann's theory to rest.

The idea was to some extent anticipated in an 1865 article by Francis Galton, published in Macmillan's Magazine, which set out a weak version of the concept. In 1889 Weismann wrote to acknowledge that "You have exposed in your paper an idea which is in one essential point nearly allied to the main idea contained in my theory of the continuity of germ-plasm".[5]

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order (Biology)

order n.  20. Biology A taxonomic category of organisms ranking above a family and below a class. -- AHTD

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Phylum or Division

-- UKT 2008

"The plant kingdom is divided into divisions (phyla). Zoologists divide the animal kingdom into phyla, and for purposes of conformity of category names between the two branches, some biologists and botanists have adopted for plants the term phyla (sing. phylum -- UKT) in place of division. The term division (phylum) is prescribed by the rules of nomenclature to represent the category of highest magnitude within the plant kingdom, whereas phyla is not mentioned." (see Major Categories)

I am not a biologist, but a chemist. I am a layperson as far as biology is concerned. To me, the word 'division' is more general than 'phylum', and has more than one meaning. However, 'phylum' is not in every-day vocabulary and can have only one meaning. I prefer 'phylum' as a technical term, and I have changed 'division' to 'phylum' in this paper.

phylum n. pl. phyla 1. BiologyA primary division of a kingdom, as of the animal kingdom, ranking next above a class in size. See note at taxonomy . 2. Linguistics A large division of possibly genetically related families of languages or linguistic stocks. -- AHTD

subphylum n. pl. subphyla Biology 1. A taxonomic category of related organisms ranking between a phylum and a class. -- AHTD

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pistil

pistil n. 1. The female, ovule-bearing organ of a flower, including the stigma, style, and ovary. [French from New Latin pistillum from Latin pestle (from its shape)] -- AHTD

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taxon 

From Wikipedia: http://en.wikipedia.org/wiki/Taxon 121230

A taxon (plural: taxa) is a group of one (or more) populations of organism(s), which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement. Defining what belongs or does not belong to such a taxonomic group is done by a taxonomist with the science of taxonomy. It is not uncommon for one taxonomist to disagree with another on what exactly belongs to a taxon, or on what exact criteria should be used for inclusion.

Taxonomists sometimes make a distinction between "good" (or natural) taxa and others that are "not good" (or artificial). Today it is common to define a good taxon as one that reflects evolutionary (phylogenetic) relationships, but this is not mandatory.

A taxon may be given a formal scientific name, the application of which is governed by one of the Nomenclature Codes, which set out rules to determine which scientific name is correct for that particular grouping.

Advocates of phylogenetic nomenclature, using cladistic methods, require taxa to be monophyletic, consisting of all descendants of some ancestor. They generally do not refer to taxa as their basic unit, but to " clades," a clade being a special form of taxon. However, even in traditional nomenclature, few taxonomists of our time would establish new taxa that they know to be paraphyletic. [1] A famous example of a widely accepted taxon that is not also a clade is the " Reptilia."

UKT: The term "paraphyletic" from "paraphyly" is also used in historical linguistics. See Wikipedia:
#1. http://en.wikipedia.org/wiki/Paraphyletic 121230
#2. http://en.wikipedia.org/wiki/Tree_model 121230
The following is taken from #1.
   "The concept of paraphyly has also been applied to historical linguistics, where the methods of cladistics have found some utility in comparing languages. For instance, the Formosan languages form a paraphyletic group of the Austronesian languages as the term refers to the nine branches of the Austronesian family that are not Malayo-Polynesian and restricted to the island of Taiwan. [17]

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tribe

From Wikipedia: http://en.wikipedia.org/wiki/Tribe-biology 121229 

In biology, a tribe is a taxonomic rank between family and genus. [1] [2] It is sometimes subdivided into subtribes.

In zoology, some examples include the tribes Caprini (goat-antelopes), Hominini (hominins), Bombini (bumblebees), and Thunnini (tunas). In botany, examples include the tribes Acalypheae and Antidesmeae.

UKT: End of Wikipedia stub

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