Author: Jan Scholten
Taxonomy is the classification of plants, animals, living creatures in groups.
Classification is sorting things into groups or categories. Categories can be grouped into larger groups and so on. The more things you let a category include, the less concrete it becomes. The biggest group in botany is the group of “plants”. Eventually, you have a category labeled "stuff". Mathematically the grouping can be visualized by the theory of sets. In the case of taxonomy the species or group can only belong to one group.
Categories can be ordered by inclusiveness. More inclusive categories have higher ranks and less inclusive categories have lower ranks. As we go down this list, the categories become less inclusive and of lower rank.
D. Qualities Criteria.
Qualities or criteria define categories. Qualities are the “key characteristics”, the “features” used to circumscribe the categories. Qualities must be presented so that they mean the same thing to everyone.
Qualities must be chosen in such a way that they define the most meaningful characteristics of groups. As qualities are used.
E. Example of Categories or Groups.
Rank Quality Example.
1. Things tables, houses, boats, buses.
2. Moving boats, buses, cars.
3. With wheels buses, bicycles, skates, airplanes, trains.
4. Ground transport buses, cars, bicycles, trains.
5. Carries many persons buses, cars, trains.
6. Runs on rails trains.
Linnaeus made the first classification of plants. This is still the basis of the taxonomy together with his nomenclature. He ordered the species in genus’s and families. Later the families were ordered in order, classes and divisions. Total orderings of plants have been made by Takthajan (1980), Dahlgren (1983), Thorne (1983, 1992), Cronquist (1981, 1988) and Stebbins. These classifications have many similarities but they also differ in many respects in respect to the orders, classes and divisions. Recently a new classification has been developed, the Apg classification, by the "Angiosperm Phylogeny Group". This is based on DNA analysis and is seen as the most reliable.
What has to be classified as members of groups are species. Cronquist defines a species as (1988): "Species are the smallest groups that are consistently and persistently distinct and distinguished by ordinary means. ".
Many qualities have been used in the development of botanical taxonomy. They reflect the development of science as a whole. The most useful tools in the study of systematics in botany have been as follows.
1. Anatomy: ± 1800: morphology, anatomy: This is the eldest criterion for classification and for a long time has been almost the sole criterion. A good example is the “umbrella” form of the flowers of the family Apiaceae (former Umbelliferae). Taste, smell and effects on living creatures were used as additional information.
2. Embryology: microsporogensis, megasporogensis, gametophytes, fertilization, endosperm, embryo, seed coats.
3. Chromosome numbers: 1920's.
4. Cytology, palynology, paleobotany, ecology.
5. Comparative garden studies: 1940's.
6. Palynology: 1950's.
7. Phenetics: 1960's.
8. Biochemical systematics: 1970's: chemosystematics.
9. Cladistics: 1980's.
10. Chloroplast DNA and RNA: 1990's: genetic sequencing data.
D. Development of taxonomy.
As expressed above taxonomy has had its own evolution. This evolution has been influenced mostly by new insights and by new kinds of evidence. One can distinguish.
1. Phenetic taxonomy: Present nature of organisms.
Before evolutionary theories organisms were placed in "buckets" by common attributes, relying upon appearance (phenotype). A key developer in our present system was Carolus Linnaeus (1707-1778). In modern times, this method is made more quantitative through computer analysis of many features.
2. Phylogenetic taxonomy: Evolutionary relationships of organisms.
This system arose in the late nineteenth century with evolutionary theory. Here groupings are made by presumed ancestry.
3. Cladistics (from Greek klados branch) taxonomy: Branching order by which organisms have derived from an ancestral stem.
This scheme arose in the 1970's to use a more objective approach based on DNA, proteins, etc. Overall similarities are not important.
This classification is based on various recently published phylogenetic analyses and it is equivalent to "An ordinal classification for the families of flowering plants", as submitted for publication in the Annals of the Missouri Botanical Garden by the "Angiosperm Phylogeny Group".
Several families are deliberately not classified to order to avoid undesirable non-monophyletic taxa as well as redundant monofamilial taxa. Note that the Linnaean categories of order and family are only to be conceived as a convenient reference to hierarchical relationships. Groups of the same rank are not comparable units unless they are sister groups.
The taxonomy reflects the evolution of the plants. This is expressed in the tree like form of the taxonomy. It can also been seen in the circular form, the centre being the eldest part of the evolution and the more eccentric parts the recent developments of the plants in the evolution.
The qualities that characterize late evolution are (Besseyan principles).
1. Woody to non-woody; perennial to annual; terrestrial to aquatic or epiphytic, saprophytic and parasitic conditions.
2. Cylindric to scattered vascular bundle(s).
3. Alternate leaves to opposite or whorled; simple leaves to compound leaves.
4. Bisexual flowers to unisexual in most instances.
5. Perianth parts many and spirally arranged to few and whorled with actinomorphic (regular) to zygomorphic (irregular) flowers.
6. Separate perianth parts, poorly differentiated in to sepals and petals, to fused perianth parts, sharply differentiated; petalous to apetalous.
7. Many separate stamens to few united stamens.
8. Hypogyny to perigyny and epigyny (e. g. superior to inferior).
9. Numerous and separate carpels to few and fused carpels.
10. Pollen grains with one pore to grains with two or more pores.
11. Small embryo in abundant endosperm in arillate seeds to large embryo without endosperm in non-arillate seeds.
12. Axile placentation to free-central placentation.
13. Single fruits to aggregate fruits; capsules to drupe or berry.
14. Pro-anthocyanin compounds to anthocyanin compounds.
In summary: angiosperm evolution has been one of reduction in number, fusion and specialization of parts coupled with changes in symmetry justification: evolution is the cause of a natural system of classification; natural classification will represent the hierarchy of evolution. Classifications are based on features that seem to reflect common ancestry.
It is typical that the majority of the old classifications are confirmed by new criteria of classification. Although there are changes in the higher groupings, the majority of families and groupings are the same for the newest Apg classification as it was with that of Linnaeus. This is a confirmation of the idea that groups are not made by change, that they are not just arbitrary or artificial. An artificial order would lead to many equivalent orders instead of one generally accepted order.
Taxonomy is useful because it has predictive value.
a. Qualities of a group can be applied to an unfamiliar plant that is a member of the group.
b. Qualities of a few members of a group can lead to some good guesses about the group as a whole.
Order Number Name Ending Example.
Creatures All creations.
1 Kingdom Plants All plants.
2 Division 1 Angiospermae mae, phyta Flowering plants.
3 Subdivision Eudicots cots Dicotyledons.
4 Class 5 Asteridae ids, opsida Class of Aster-like plants.
5 Subclass 19 EuAsteridae 2 ids, idae Subclass of Aster-like plants.
6 Order 201 Asterales ales Order for Aster-like plants.
7 Family 552 Asteraceae aceae Family for Aster-like plants.
8 Subfamily Heliantheae eae Sunflower like plants.
9 Genus 13900 Arnica us, um, a Genus of all Arnica’s.
10 Species 255000 Arnica montana Specific Arnica.