What is classification?
The arrangement of plants into different groups and sub-groups and classes is called classification. These are classified on the basis of similarities. The characters which are used as the basis of classification are called criteria of classification.
Basis of Classification System for Plants
- Earlier, for the plant kingdom, the basis of classification was cell walls. In the two kingdom classification system, all organisms with cell walls were included in the kingdom Plantae.
- In the five-kingdom classification system, five kingdoms i.e., Monera, Protista, Fungi, Animalia, and Plantae were formed. All organisms with photosynthetic activity were included in the plant kingdom.
- Further classification of plants was based on vascular and reproductive tissues. Plants without or lacking vascular tissues were placed in Bryophyta. The plants having vascular tissues are placed in Tracheophyta.
- Tracheophyta is divided into two groups: Seed producing and non-seed producing. Seed-producing plants form group embryophyta.
- Embryophyta is further divided into two groups Gymnosperms: plants with naked seeds and Angiosperms: Plants with enclosed seeds.
- Angiosperms are further divided into monocots and dicots.
Units of Classification
The units of classification are called taxa. Each taxon is more general than the taxa below it. The members of the lower category resemble more with one another than the higher taxon. Initially, this classification system was based on appearance or morphology.
Later, there was advancement in knowledge of cytology, plant physiology, molecular biology, and genetics. So, the classification system is modified. Following units of classification are used:
1. Species
A species is a group of organisms that can interbreed freely and produce fertile offspring. The species is further subdivided
a. Sub-species:
The member of sub-species are capable of interbreeding and producing fertile offspring. The differences between subspecies are less distinct than between species.
b. Variety:
The taxonomic rank below species and subspecies is variety. It will have an appearance distinct from other varieties. And they will hybridize freely.
c. Form:
It is used for variation in a single feature within a variety. For example, round or wrinkled seed. etc.
2. Genera
Consists of one or more similar species.
3. Family:
Composed of similar genera. The genus having similar properties and other characteristics are placed under the same family.
4. Order:
Similar families form similar orders.
5. Class:
Similar orders form a class. For example, all the orders of flowering plants are placed in single class Angiospermae.
6. Phylum or Divisions:
Similar classes form phylum. Phylum is also called division in Plants, Fungi, and Algae.
7. Kingdom:
Similar phyla form a kingdom. There are two kingdoms: Kingdom Animalia and Kingdom Plantae.
Importance of Classification System
- The classification system has great importance for botany, botanists, molecular biology, genetics, etc.
- Classification arranges plants into systematic groups. It makes it easy for botanists to study and differentiate them.
- Classification provides phylogenetic linkages and relationships. So, it helps in the study of the evolution of plants.
- Different members in different taxonomic groups have similar characters. Thus, the study of morphology, anatomy, or cytology gives the idea of the structure of other members.
- Phytogeography of plants is also studied by classification.
- Different morphological, physiological, and genetic characteristics can be predicted from classification.