HISTORY OF PLANT'S CLASSIFICATION
The inherent curiosity of the human mind, the need for orderliness in knowledge, and the desire to communicate effectively has stirred interest in plant study and classification for centuries. According to Lawrence (1951), the earliest system of classification, proposed by the Greeks and herbalists, was based on the forms of plants: trees, shrubs, herbs, vines, and so on. This system prevailed from about 300 B.C. to the middle of the eighteenth century and became somewhat more elaborate as new information and concepts were incorporated. From about 1500 to 1700, gross flower characters such as ovary position (superior vs. inferior) and petal structure (petalous vs. apetalous, polypetalous vs. sympetalous, and regular vs. irregular flowers) became important. During this period, Joseph Pitton de Tournefort (1656–1708) developed the modern “genus” concept, and many of his names, including Salix, Populus, Fagus, and Acer are still valid. Another botanist, John Ray (1628–1705), developed a system based on gross morphology of plant structures. He divided plants into woody and non-woody and recognized monocots and dicots within each division. Further subdivisions were based on fruit type— coniferous, berry or berry-like, nut-bearing, and so forth—and leaf and flower characters. This approach subsequently formed the basis for the more modern classification systems developed by Bernard de Jussieu and Carolus Linnaeus.
Carolus Linnaeus (1707–1778) is considered the father of modern plant and animal taxonomy. Prior to 1700, lengthy descriptive names were assigned to plants and it was difficult to relocate plants that had been previously described. Linnaeus was a prolific writer and an extraordinary taxonomist. In Hortus uplandicus (1730), he proposed what he called a sexual system of plant classification. This system was a major contribution because it was simple and based on plant taxonomic relationships. However, the system was artificial, because the emphasis was primarily on numerical relationships of flower parts; thus, similar plants often fell intowidely separated classes. Later, in Genera plantarum (1737), he revised this system and included a list of natural plant orders and their genera. The publication of his famous Species plantarum in 1753 is considered the starting point of present-day nomenclature (naming of plants). In this treatise, Linnaeus proposed assigning two names, a Latin binomial, to each plant. Many of the names he assigned to plants during his lifetime remain valid and in use today, as can be seen by observing the species names found in the chapters of Parts II and III. Near the end of the eighteenth century, systems based on form (morphological) relationships began to appear. These new systems were called natural systems, as plants having similar combinations of characters were placed together. They were not based on evolutionary relationships, but ordered plants along more natural lines while serving as an aid in identification. The taxonomists of this period included Antoine Laurent de Jussieu (1748–1836), three generations of de Candolles, the most important being Augustin Pyrame, and two botanists who collaborated on a system, George Bentham (1800–1884) and Sir Joseph Dalton Hooker (1817–1911). There was a marked similarity in the systems of these taxonomists. In particular, all were based on the concept of species immutability; that is, species were created and therefore they could not change. However, the systems still represented scientific progress.
The systems of de Jussieu and Bentham and Hooker divided the seed plants into three classes: Dicotyledoneae,Monocotyledoneae and Gymnospermae. The Dicotyledoneae class was further divided in the Polypetalae (corolla of separate petals), Gamopetalae (corolla of fused or partially fused petals, sympetalae), andMonochlamydeae (no petals, apetalous). These classes appeared relatively natural, and the divisions remained part of taxonomic classification until about 40 years ago (refer to Harlow et al. 1978). The theories of Alfred Wallace and Charles Darwin around the middle of the nineteenth century began a new period in taxonomic investigation and classification. The new systems were based on phylogeny or on the evolutionary development and genetic relationships between plants.
The Engler and Prantl system of classification was developed during this period, although it was not phylogenetic in a modern sense. This system divided the seed plants into the Gymnospermae and the Angiospermae, the latter being divided into the Monocotyledoneae and the Dicotyledoneae. The dicots were then divided into subclasses (Apetalae, Gamopetalae, and Polypetalae). Each subclass was divided into orders of presumably related families. There was some objection to the system, but it was widely accepted because Engler and Prantl applied it to the plants of the world, the result being a 20-volume work. Charles Bessey (1845–1915) was the first American taxonomist to make a contribution to classification by developing a systemthat was truly phylogenetic (Lawrence 1951). In essence, he realigned the system developed by Bentham and Hooker according to evolutionary principles but also included some of the principles of Engler and Prantl. Other systems that were developed include one by John Hutchinson of England, which is closely alignedwith that of Bentham and Hooker and that of Bessey, and one by Oswald Tippo of the University of Illinois (Fuller and Tippo 1954), which incorporated the latest developments in phylogeny.
The classification systems of Bentham and Hooker, Engler, Bessey, Hutchinson, and Tippo are in use throughout the world. The Engler systemis widely used in herbaria in theUnited States, but the other systems are more accurate. No doubt these systems will continue to be revised as new scientific information becomes available. The most recent classification system was proposed by Cronquist (1981). He considered only the division Magnoliophyta angiosperms), which was split into two classes: Magnoliopsida (dicots; six subclasses) and Liliopsida(monocots;five subclasses).The species are clustered into these subclasses based on best available evolutionary evidence, so that some orders and families once considered relatively close have now been separated. Perhaps the most notable change is the breaking up of the old Amentiferae (catkin bearing woody plants); the Fagaceae (oak, beech), Juglandaceae (hickory, walnut), and Betulaceae (birch) families are in subclass Hamamelidae, while the Salicaeae (aspen, cottonwood, poplar) has been placed in subclass Dilleniidae, because although the inflorescences are similar, the origins of the unisexual flowers are apparently different. The Cronquist system has been readily accepted. Before leaving this short historical account of the development of taxonomy, the reader should contemplate for a moment the problems and frustrations encountered by early botanists. Prior to the modern systems, it must have been extremely difficult to describe, identify, and classify plants. It is likely that for a long period, every new plant added to the list of known species somehow changed the ideas and the concepts of the botanist, and the classification system changed accordingly. Consider the problem of keeping track of plants and their names before the standardized system of nomenclature was developed. Letters to distant colleagues must have been filled with long descriptions and probably many sketches. As compared with the effort required during the early 1700s, the identification of an unknown plant and relocation of specimens within a herbarium is now relatively simple.
The inherent curiosity of the human mind, the need for orderliness in knowledge, and the desire to communicate effectively has stirred interest in plant study and classification for centuries. According to Lawrence (1951), the earliest system of classification, proposed by the Greeks and herbalists, was based on the forms of plants: trees, shrubs, herbs, vines, and so on. This system prevailed from about 300 B.C. to the middle of the eighteenth century and became somewhat more elaborate as new information and concepts were incorporated. From about 1500 to 1700, gross flower characters such as ovary position (superior vs. inferior) and petal structure (petalous vs. apetalous, polypetalous vs. sympetalous, and regular vs. irregular flowers) became important. During this period, Joseph Pitton de Tournefort (1656–1708) developed the modern “genus” concept, and many of his names, including Salix, Populus, Fagus, and Acer are still valid. Another botanist, John Ray (1628–1705), developed a system based on gross morphology of plant structures. He divided plants into woody and non-woody and recognized monocots and dicots within each division. Further subdivisions were based on fruit type— coniferous, berry or berry-like, nut-bearing, and so forth—and leaf and flower characters. This approach subsequently formed the basis for the more modern classification systems developed by Bernard de Jussieu and Carolus Linnaeus.
Carolus Linnaeus (1707–1778) is considered the father of modern plant and animal taxonomy. Prior to 1700, lengthy descriptive names were assigned to plants and it was difficult to relocate plants that had been previously described. Linnaeus was a prolific writer and an extraordinary taxonomist. In Hortus uplandicus (1730), he proposed what he called a sexual system of plant classification. This system was a major contribution because it was simple and based on plant taxonomic relationships. However, the system was artificial, because the emphasis was primarily on numerical relationships of flower parts; thus, similar plants often fell intowidely separated classes. Later, in Genera plantarum (1737), he revised this system and included a list of natural plant orders and their genera. The publication of his famous Species plantarum in 1753 is considered the starting point of present-day nomenclature (naming of plants). In this treatise, Linnaeus proposed assigning two names, a Latin binomial, to each plant. Many of the names he assigned to plants during his lifetime remain valid and in use today, as can be seen by observing the species names found in the chapters of Parts II and III. Near the end of the eighteenth century, systems based on form (morphological) relationships began to appear. These new systems were called natural systems, as plants having similar combinations of characters were placed together. They were not based on evolutionary relationships, but ordered plants along more natural lines while serving as an aid in identification. The taxonomists of this period included Antoine Laurent de Jussieu (1748–1836), three generations of de Candolles, the most important being Augustin Pyrame, and two botanists who collaborated on a system, George Bentham (1800–1884) and Sir Joseph Dalton Hooker (1817–1911). There was a marked similarity in the systems of these taxonomists. In particular, all were based on the concept of species immutability; that is, species were created and therefore they could not change. However, the systems still represented scientific progress.
The systems of de Jussieu and Bentham and Hooker divided the seed plants into three classes: Dicotyledoneae,Monocotyledoneae and Gymnospermae. The Dicotyledoneae class was further divided in the Polypetalae (corolla of separate petals), Gamopetalae (corolla of fused or partially fused petals, sympetalae), andMonochlamydeae (no petals, apetalous). These classes appeared relatively natural, and the divisions remained part of taxonomic classification until about 40 years ago (refer to Harlow et al. 1978). The theories of Alfred Wallace and Charles Darwin around the middle of the nineteenth century began a new period in taxonomic investigation and classification. The new systems were based on phylogeny or on the evolutionary development and genetic relationships between plants.
The Engler and Prantl system of classification was developed during this period, although it was not phylogenetic in a modern sense. This system divided the seed plants into the Gymnospermae and the Angiospermae, the latter being divided into the Monocotyledoneae and the Dicotyledoneae. The dicots were then divided into subclasses (Apetalae, Gamopetalae, and Polypetalae). Each subclass was divided into orders of presumably related families. There was some objection to the system, but it was widely accepted because Engler and Prantl applied it to the plants of the world, the result being a 20-volume work. Charles Bessey (1845–1915) was the first American taxonomist to make a contribution to classification by developing a systemthat was truly phylogenetic (Lawrence 1951). In essence, he realigned the system developed by Bentham and Hooker according to evolutionary principles but also included some of the principles of Engler and Prantl. Other systems that were developed include one by John Hutchinson of England, which is closely alignedwith that of Bentham and Hooker and that of Bessey, and one by Oswald Tippo of the University of Illinois (Fuller and Tippo 1954), which incorporated the latest developments in phylogeny.
The classification systems of Bentham and Hooker, Engler, Bessey, Hutchinson, and Tippo are in use throughout the world. The Engler systemis widely used in herbaria in theUnited States, but the other systems are more accurate. No doubt these systems will continue to be revised as new scientific information becomes available. The most recent classification system was proposed by Cronquist (1981). He considered only the division Magnoliophyta angiosperms), which was split into two classes: Magnoliopsida (dicots; six subclasses) and Liliopsida(monocots;five subclasses).The species are clustered into these subclasses based on best available evolutionary evidence, so that some orders and families once considered relatively close have now been separated. Perhaps the most notable change is the breaking up of the old Amentiferae (catkin bearing woody plants); the Fagaceae (oak, beech), Juglandaceae (hickory, walnut), and Betulaceae (birch) families are in subclass Hamamelidae, while the Salicaeae (aspen, cottonwood, poplar) has been placed in subclass Dilleniidae, because although the inflorescences are similar, the origins of the unisexual flowers are apparently different. The Cronquist system has been readily accepted. Before leaving this short historical account of the development of taxonomy, the reader should contemplate for a moment the problems and frustrations encountered by early botanists. Prior to the modern systems, it must have been extremely difficult to describe, identify, and classify plants. It is likely that for a long period, every new plant added to the list of known species somehow changed the ideas and the concepts of the botanist, and the classification system changed accordingly. Consider the problem of keeping track of plants and their names before the standardized system of nomenclature was developed. Letters to distant colleagues must have been filled with long descriptions and probably many sketches. As compared with the effort required during the early 1700s, the identification of an unknown plant and relocation of specimens within a herbarium is now relatively simple.
0 comments:
Post a Comment