Biology Classification Systems in Plant Kingdom

### Topics covered

star Introduction
star Systems of Classification
a) Artificial system of Classification
b) Natural system of Classification
c) Phylogenetic system of Classification
star Types of Taxonomy
a) Numerical Taxonomy
b) Cytotaxonomy
c) Chemotaxonomy

### INTRODUCTION

●Our understanding of the plant kingdom has changed over time.

● Fungi and members of the Monera and Protista having cell walls (which were peviously included in Kingdom Plantae in two kingdom classification system) have now been excluded from Plantae.

star So, the cyanobacteria that are also referred to as blue green algae are not ‘algae’ any more.

●According to Whittaker’s Five kingdom Classification, Plantae includes following five divisions:
color{Green} "Algae (Thallophyta), Bryophytes, Pteridophytes, Gymnosperms and Angiosperms".

### SYSTEMS OF CLASSIFICATION

Classifications use orderly ways to express information and, depending upon their objectives, can be:
color{Green}"Artificial, Natural, or Phylogenetic (phyletic)".

Thus the three major classification systems within angiosperms which have been proposed are as follows.

### ARTIFICIAL CLASSIFICATION SYSTEMS

● Used only color{Green}"gross superficial morphological characters" such as habit, colour, number and shape of leaves, etc.

● They were based mainly on vegetative characters or on the androecium structure (system given by color{Green} "Linnaeus").

● All the plants in a single group share the same characteristics, but they are not closely related to one another genetically.

● E.g : Important floras sometimes group plants using color of their flowers.

color{Maroon}"Advantages":
●It is color{Green}"easy to remember" as only a few characters are used.

●The traits considered were practically important to humans.

color{Maroon}"Disadvantages":
● This system use only a few color{Green}"superficial characters" which leads to many different organisms being grouped together.

● It does not represent natural and phylogenetic relationships.

●They separated only the color{Green}"closely related species" since they were based on a few characteristics.

● Also this system was not acceptable as it gave color{Green}"equal weightage" to vegetative and sexual characteristics inspite of the fact that often the vegetative characters are more easily affected by environment.

● They provide only a few clues about relationships among the taxa and hence are not predictive.

### NATURAL CLASSIFICATION SYSTEM

● It is also called as color{Green}"phenetic system of classification".

● It is based on the color{Green}"natural affinities" among the organisms and consider the external features as well as internal features, like ultrastructure, anatomy, embryology and phytochemistry.

● This classification for flowering plants was given by color{Green}"George Bentham and Joseph Dalton Hooker" and is widely popular even today.

color{Brown}"Advantages" :
● Only related organisms are placed in the same group whereas unrelated organisms are kept in separate groups.

● It demonstrates natural relationships among the organisms.

●Plants which are grouped together have many of the same characteristics and thus,are color{Green}"highly predictive". That is, by listing the characteristics of a plant, one can predict the natural group to which it belongs.

color{Brown}"Disadvantages":

●More emphasis is given on the natural characters.

●Also several related families get placed separately whereas unrelated families get placed together.

●It does not represent phylogenetic relationships among organisms

### Phylogenetic Classification Systems

● Based on the color{Green}"evolutionary" as well as color{Green}"genetic relationships" between the various organisms and is completely acceptable.

● This assumes that organisms belonging to the same taxa are related to one another by a color{Green}"common ancestor".

● Now information from many other sources is also used to help resolve difficulties in classification, especially when there is no supporting fossil evidence.

● Previous classifications were primarily based upon plant anatomy and morphology with great emphasis upon reproductive morphology.
Today, additionally the techniques of color{Green}"biochemistry and molecular biology" are used by taxonomists to add details of internal organization

### TYPES OF TAXONOMIES

For the suitability in studies various categories have branched out in taxonomy. These are as follows.

### NUMERICAL TAXONOMY

● It is based on all observable characteristics and is now carried out using color{Green}"computers".

● color{Green}"Quantitative assessments" are made based upon the similarities and differences between various taxa.

● color{Green}"Number and codes" are assigned to all the characters and the data are then processed.

● In this way each character is given color{Green}"equal importance" and at the same time hundreds of characters can be considered.

### CYTOTAXONOMY

● Based on color{Green}"cytological information" like chromosome number, structure and behaviour, especially during cell division (mitosis).

● Chromosome studies are used to trace lineages.

● Example
star color{Green}"Chromosome number" is constant for a species, e.g., 48 in apes, 46 in man, 20 in maize and 16 in onion. So, information on the chromosome number can indicate the species being studied.

star The color{Green}"pairing and banding patterns" of the chromosomes are used to understand the relationships between different species e.g., evolution of humans from apes shows a particular difference in banding pattern.

### CHEMOTAXONOMY

●It is the system based upon the presence and absence of various color{Green}"chemical constituents" (proteins, amino acids, enzymes, hormones, etc.), specific chemicals (secondary metabolites) which is used to demonstrate relationships between various organisms.

● Mainly color{Green}"chemical and protein tests" are performed to understand relationships between different organisms via the chemicals they produce.

● For example, 35 families of plants been characterized by the presence of chemical compound –color{Green}"raphide" within them.