Taxonomic order

“ I hope that I have succeeded in showing that the difference between elementary species, or, as they are often called, smaller or subspecies, on the one hand and varieties on the other, is quite a marked one. However, in order to recognize this principle it is necessary to limit the term variety, to those propagating themselves by seed and are of pure and not of hybrid origin. ”

“ They argued taxonomy needed rules around what should be called a species, because currently there are none. They wrote:
for a discipline aiming to impose order on the natural world, taxonomy (the classification of complex organisms) is remarkably anarchic [...] There is reasonable agreement among taxonomists that a species should represent a distinct evolutionary lineage. But there is none about how a lineage should be defined. ‘Species’ are often created or dismissed arbitrarily, according to the individual taxonomist's adherence to one of at least 30 definitions. ”

“ Whenever taxonomists increase their data (individuals studied) to a volume comparable with that on which the best research in other fields has been based, pursue their comparisons of related species as persistently as the geneticists have compared related generations of individuals, and strive towards interpretations of their data which shall be coördinated with the findings from other fields of biology, we shall have a taxonomic science that cannot fail to command the respect of students. ”

“ In many cases a Linnaean species has been split up till it became, first, a genus, then a family, and, in some cases, an order. What one naturalist considers a species is considered by another a genus containing several species, and, vice versa, the species of one authority is described as merely a variety by another. The older naturalists might have said with truth: we do not know what the species are, but we are quite certain that whatever they are they have never undergone any change in their distinguishing characters. ”

“ As a rule, however, formations most frequently show endemic habitat forms and species, more rarely endemic genera; regions and provinces commonly exhibit endemic species and genera, rarely endemic families; while zones and hemispheres contain endemic orders as well as families. This correspondence is readily seen to depend primarily upon the fact that increased differentiation in the taxonomic sense is a concomitant of the increased invasion of endemic species, measured in terms of distance and difference in habitat. ”

“ Variety comes in upon occasion. For, although a species may have no recognized varieties, a genus implies at least one species belonging to it; every genus is of some order, and every order of some class.
533. But these grades by no means exhaust the resources of classification, nor suffice for the elucidation of all the distinctions which botanists recognize. In the first place, a higher grade than that of class is needful for the most comprehensive of divisions, that of all plants into the two Series of Phanerogamous and Cryptogamous (6) ”

“ In fact, it is anticipated that transparent governance of a unified global list will enhance the scientific reputation of taxonomy by showcasing the strengths and merits of both the decision-making process and the underlying taxonomic research on which the list is based.
6. The set of criteria considered sufficient to recognise species boundaries may appropriately vary between different taxonomic groups but should be consistent when possible
There is no universally accepted definition of a species. ”

“ Because taxonomy is the foundation for much of the dialog and research in evolutionary biology, there must be an unambiguous taxonomic system in which one term is linked to one concept. In contrast to this ideal, homonymy and redefinition are prevalent in the taxonomy of eukaryotes, often as the result of premature introduction or redefinition of taxa (see above; Figure 3) . Emerging hypotheses benefit the community by sparking new research to test the hypothesis, but they also introduce ambiguity. ”

“ In order to meet this difficulty we must recognize two sorts of species. The systematic species are the practical units of the systematists and florists, and all friends of wild nature should do their utmost to preserve them as Linnaeus has proposed them. These units however, are not really existing entities; they have as little claim to be regarded as such as genera and families. ”

“ The number of known species having much increased, and the language of Linnæus and the principles of Jussieu having much augmented the facilities for the study of affinities, botanists have become aware that the species of a genus and the genera of an order can be collected into intermediate groups 347 as natural and as well defined as the genera and orders themselves, and names are required for these subordinate groups as much as for the genera and orders. ”

“ In arranging the species of a great natural order they are always divided into first large and then progressively smaller and smaller groups. The order is divided into coordinate families, each family into coördinate genera, and each genus into species which are also coordinate. Usually there are found to be more subdivisions than these and we have in botany at least, suborders, subfamilies, tribes, subtribes, and subgenera. Even species have their varieties, and in some sciences, particularly in ornithology, these are called subspecies and have a special significance. ”

“ While interpretation will always play a part in taxonomy, the general use of experiment will leave much less opportunity for the personal equation than is at present the case. Taxonomy, like descriptive botany, is based upon the species, but, while there may exist a passable kind of descriptive botany, there can be no real taxonomy as long as the sole criterion of a species is the difference which any observer thinks he sees between one plant and another. The so-called species of to-day range in value from mere variations to true species which are groups of great constancy and definiteness. ”

“ A perfect taxonomy is one which would perfectly express all the facts in the evolution and development of the various forms. It would recognize all the evidence from the three ancestral documents, palæontology, morphology, and ontogeny. It would consider structure and form independently of adaptive or physiological or environmental modifications. It would regard as most important those characters which had existed longest unchanged in the history of the species or type. It would regard as of first rank those characters which appear first in the history of the embryo. ”

“ Now it is manifest, that in order to make crosses, distinct individual plants are to be chosen, and that the variability of the wild species may be of very great importance. [59] Among the range of elementary species those should be used which not only possess the desired advantages in the highest degree, but which promise the best results in other respects or their earliest attainment. The fuller our knowledge of the elementary species constituting the systematic groups, the easier and the more reliable will be the choice for the breeder. ”

“ In this sense, according to our theory, there has been a gradual passage (the steps not being wider apart than our domestic varieties) between the species of the same genus, between genera of the same family, and between families of the same order, and so on, as far as facts, hereafter to be given, lead us; and the number of forms which must have at former periods existed, thus to make good this passage between different species, genera, and families, must have been almost infinitely great. ”

“ The suggestion of applying qualifying terms to each and all of the varieties of a subspecifically divided species is most wholesome, and should be applied to the scientific as well as the vernacular nomenclatural system. Modern subspecific ideas should not recognize the superiority of one variety over another without good evolutionary reasons for so doing. Why call one form a species and the rest varieties just because one of them had, of necessity, to be discovered first? ”

“ To what extent these hints for the discrimination of species will be found to avail in practice, it is difficult to say, but it seems desirable that they should speedily be brought to the test of experience, since there is no genus, of the same extent, in which it is so difficult to determine the species. ”

“ Though we can not indicate the distinctive properties of the Kind, we may indicate its nearest natural affinities, by incorporating into its name the name of the proximate natural group of which it is one of the species. On this principle is founded the admirable binary nomenclature of botany and zoology. In this nomenclature the name of every species consists of the name of the genus, or natural group next above it, with a word added to distinguish the particular species. ”

“ From a further consideration of the foregoing principles it will be seen that all existing species are held to be descended by true generation from pre-existing species, and that, consequently, all the relationships we observe between species are explained by community of origin. The most natural system of classification is, therefore, that which best reveals the scheme of descent, or, as it is termed, the phylogeny, of the group of organisms classified. ”

“ The variety: Any plant grouping within a single botanical taxon of the lowest known rank, which grouping, irrespective of whether the conditions for the grant of a breeder’s right are fully met, can be defined by the expression of the characteristics resulting from a given genotype or combination of genotypes, distinguished from any other plant grouping by the expression of at least one of the said characteristics and considered as a unit with regard to its suitability for being propagated unchanged. ”

“ Vertical lines indicate the consensus standard error. (P–T) Frequency distribution of the number of subordinate taxa at different taxonomic levels. For display purposes we present only the data for Animalia; lines and test statistics are from a regression model fitted with a power function. Changes in taxonomic effort
Taxonomic effort can be a strong determinant of species discovery rates [14] . Hence the estimated asymptotes from the temporal accumulation curves of higher taxa (dotted horizontal line in Figure 1A–1E) might be driven by a decline in taxonomic effort. ”

“ A closer scrutiny of the facts, however, makes the term hybridism less isolated and more vague. The words species and genus, and still more subspecies and variety, do not correspond with clearly marked and sharply defined zoological categories, and no exact line can be drawn between the various kinds of crossings from those between individuals apparently identical to those belonging to genera universally recognized as distinct. ”

“ The system of binomial nomenclature has led to the development of the science of taxonomy, the systematic classification and naming of plants and animals according to their relationships.
THE UNITS OF CLASSIFICATION
The world of organic life has been divided into the plant and animal kingdoms. These kingdoms have been further divided into larger divisions called phyla (from the Greek word phylon, a race) . Each phylum is composed of organisms with certain characteristics in common. For example, all animals with a spinal cord (or notochord) are assigned to the phylum Chordata. ”

“ Ontogenetic development is lost sight of in the march of phylogenetic development. The individual is merged in the species, the species in the genus, the order, the class, and all are finally swallowed up in the tout ensemble of organized existence. ”

“ To make the denotation of zoological names precise, exact workers are endeavouring to associate the conception of types with names, a process which can be made simple and definite with new work, but which presents great difficulties in the attempt to apply it to existing terms. Every family should have designated one of its genera as the type genus, every genus a type species and so forth. In the case of species or sub-species the type is a single specimen, either the only one before the author when writing his description, or one definitely selected by him, the others being paratypes. ”

“ Some species of animals are not represented by male individuals: and in some all the individuals are hermaphrodites, as explained in chapter XIV.
[6] Each of these higher groups has a proper name composed of a single word. In the case of no group except the species is a name-word ever duplicated. Each genus, family, order, or higher group has a name-word peculiar to it, and belonging to it alone.
[7] In some Protozoa a number of similar cells temporarily unite to form a colony, but each cell may still be regarded as an individual animal. ”

“ Very few of the genera of plants, or even of the families, can be pronounced with certainty to be Kinds. The great distinctions of Vascular and Cellular, Dicotyledonous or Exogenous and Monocotyledonous or Endogenous plants, are perhaps differences of kind; the lines of demarcation which divide those classes seem (though even on this I would not pronounce positively) to go through the whole nature of the plants. But the different species of a genus, or genera of a family, usually have in common only a limited number of characters. ”

“ We here regard species alone as entitled to distinct botanical appelation; it has been suggested that races may be indicated numerically.
Other than the omission of descriptions of varieties, the general system of classification used in the first edition has been maintained in the second. A few new family groups and a number of genera have been separated or distinguished from their congeners. ”