Classification of Plant Kingdom
Table of Contents
CLASSIFICATION OF PLANT KINGDOM
CLASSIFICATION:
It is the arrangement of plants into groups having common characteristics. These groups are arranged into systems.
The Linnaean classification groups organisms into species, genera, families, and higher taxonomic groups on the basis of visible resemblances, while other systems may use other determining factors, e.g. the molecular relationships among the groups.
INTRODUCTION:
Plants are one of the five main groups of living things. These groups are called kingdoms. The plant kingdom includes such living things as grasses, trees, ferns, bushes, and flowers. Botanists, the scientists who study plants, have counted more than 300,000 species (kinds) of plants.
The many species of organisms in the plant kingdom are divided into several phyla, or divisions, totaling about 260,000 species. The bryophytes are a diverse assemblage of three phyla of nonvascular plants, with about 16,000 species, that includes the mosses, liverworts, and hornworts. Bryophytes lack a well-developed vascular system for the internal conduction of water and nutrients and have been called nonvascular plants. It takes two generations to complete the plant life cycle (Alternation of Generations). The familiar leafy plant of bryophytes is the sexual, or gamete-producing, generation of the life cycle of these organisms. Because of the lack of a vascular system and because the gametes require a film of water for dispersal, bryophytes are generally small plants that tend to occur in moist conditions, although some attain large size under favorable circumstances and others (usually very small) are adapted to desert life.
The other phyla are collectively termed vascular plants or tracheophytes. Vascular tissue is an internal conducting tissue for the movement of water, minerals, and food. There are two types of vascular tissue: xylem, which conducts water and minerals from the ground to stems and leaves, and phloem, which conducts food produced in the leaves to the stems, roots, and storage and reproductive organs. Besides the presence of vascular tissue, tracheophytes contrast with bryophytes in that tracheophyte leafy plants is the asexual, or spore-producing, generation of their life cycle. In the evolution of tracheophytes, the spore-producing generation became much larger and more complex, whereas the gamete-producing generation became reduced and merely contained in the sporophyte tissue. This ability to evolve into larger and more diverse sporophytes, together with the ability of the vascular system to elevate water, freed tracheophytes from direct dependence on surface water. They were thus able to dominate all the terrestrial habitats of the Earth, except the higher Arctic zones, and to provide food and shelter for its diverse animal inhabitants.
Plant Kingdom
The kingdom Plantae accounts for the largest proportion of the earth’s biomass with its approximately 250,000 species of mosses, liverworts, ferns, flowers, bushes, vines, trees, and other plants. Aquatic and terrestrial plants are the basis of all food webs. They contribute life-supporting oxygen to the atmosphere and provide humans with the fossil fuels, medicines, and other substances so important to our present existence.
Knowledge of anatomy, genetics, and evolution has greatly advanced plant classification by providing a rational basis for this subdivision of botany. The 17th-century British naturalist John Ray divided plants into nonflowering and flowering types and flowering plants into dicots and monocots. The 18th-century Swedish botanist Carolus Linnaeus, however, provided the framework on which modern classifications are based and, just as important, a simplified system of nomenclature in which each plant is given two names: the first the name of the genus and the second the name of the species.
CRITERIA OF CLASSIFICATION:
Following are characteristics on which classification is based. These can be characters like:
- Leaf width
- Stamen number (the male reproductive organ of a flower, typically consisting of a stalk filament bearing a pollen-producing anther at its tip)
- Corolla length (the petals of a flower collectively, forming a ring around the reproductive organs and surrounded by an outer ring of sepals)
- Locule number (a small cavity, chamber, or cell in a plant or animal)
- Placentation (the way in which ovules are attached to the ovary of a plant), etc
Possessed by the organisms that may be compared, measured, counted, described or assessed
AIMS OF CLASSIFICATION:
- In the study of various organs of plants, it is noted that they vary an infinite variety of forms, structure, and kind.
- Despite, there are close similarities b/w certain plants which indicate a close relationship.
- The aim of the taxonomy is to bring naming, describing and arranging the plants in such a manner that their relationship with regards to their descent from a common ancestry is clearly indicated.
- Moreover, to arrange the plants in such a way as to give us an idea about the sequence of their evolution from simpler, earlier and more primitive types to more complex more recent and more advanced types in different periods of the earth.
BASIS OF CLASSIFICATION:
- The classification of plants is based upon certain characteristics
- We may use such feature as basis like environmental conditions, methods of obtaining food, anatomy, life history, size of the body, the color of flowers, use in daily life, geographic distribution
- On these bases, plants are distributed into the groups such as land plants, water plants, shade plans, sun plants, parasitic plants, saprophytic plants, etc.
UNITS OF CLASSIFICATION:
The sequence, generally, followed is:
Kingdom Phylum Classes Sub-classes Order Family Genera Species
1) Species:
A biological species is defined as a group of natural populations that mate and produce offspring with one another, but do not breed with other populations.
2) Genus:
Genus, < Latin, “birth, race, kind”> in biology, the category of classification of living things; specifically, a group of species closely related in structure and evolutionary origin. The position of a genus, in the classification of the kingdoms of living forms, is below family or subfamily, and above species. In the scientific name of the tiger lily, Lilium tigrinum, for example, Lilium is the genus name and tigrinum is the species name
3) Family:
Family, in biological classification, group of genera with related characteristics. The family is below the order and above the genus in biological groupings. The names of families in modern classification are usually derived from a genus of the family, called the type genus. The family names of animals always end in idae, as in Equidae, the horse family; those of plants almost always end in aceae, as in Dipsacaceae, the teasel family.
4) Order:
Families resembling each other are grouped in orders.
5) Class:
Orders are further grouped together to form class.
6) Division/ Phylum:
Phylum < Greek phulon “race”>, in biology, major category, or taxon, of organisms with a common design or organization. This design is shared by all members of the phylum, even though structural details may differ greatly because of evolution. The assumption is made by biologists that all members of a phylum have a common ancestry.
7) Kingdom:
Example:
Acacia nilotica
Kingdom: Plantae
Division: Phanerogams
Sub-division: Angeospermae
Class: Dicot
Sub-class: Polypetalae
Order: Calciflocae
Family: Fabaceae
Genus: Acacia
Species: nilotica
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