Objective

This topic gives an overview of; 

• Plantae
• Thallophyta
• Bryophyta
• Pteridophyta
• Gymnosperms
• Angiosperms

The plant Kingdom

Plantae

The first level of classification among plants depends on whether the plant body has well differentiated, distinct components. The next level of classification is based on whether the differentiated plant body has special tissues for the transport of water and other substances within it. Further classification looks at the ability to bear seeds and whether the seeds are enclosed within fruits.

Thallophyta

Plants that do not have well-differentiated body design fall in this group. The plants in this group are commonly called algae. These plants are predominantly aquatic. Examples are Spirogyra, Ulothrix, Cladophora and Chara.

Bryophyta

These are called the amphibians of the plant kingdom. The plant body is commonly differentiated to form stem and leaf-like structures. However, there is no specialised tissue for the conduction of water and other substances from one part of the plant body to another. Examples are moss (Funaria) and Marchantia.

Pteridophyta

In this group, the plant body is differentiated into roots, stem and leaves and has specialised tissue for the conduction of water and other substances from one part of the plant body to another. Some examples are Marsilea, ferns and horse-tails.

The thallophytes, the bryophytes and the pteridophytes have naked embryos that are called spores.The reproductive organs of plants in all these three groups are very inconspicuous, and they are therefore called cryptogamae, or ˜those with hidden reproductive organs.

On the other hand, plants with well differentiated reproductive tissues that ultimately make seeds are called phanerogams. Seeds are the result of the reproductive process. They consist of the embryo along with stored food, which serves for the initial growth of the embryo during germination. This group is further classified, based on whether the seeds are naked or enclosed in fruits, giving us two groups: gymnosperms and angiosperms

Gymnosperms

This term is made from two Greek words: gymno- means naked and sperma- means seed. The plants of this group bear naked seeds and are usually perennial, evergreen and woody. Examples are pines and deodar.

Angiosperms

This word is made from two Greek words: angio means covered and sperma means seed. The seeds develop inside an organ which is modified to become a fruit. These are also called flowering plants. Plant embryos in seeds have structures called cotyledons. Cotyledons are called seed leaves because in many instances they emerge and become green when the seed germinates. Thus, cotyledons represent a bit of pre-designed plant in the seed. The angiosperms are divided into two groups on the basis of the number of cotyledons present in the seed. Plants with seeds having a single cotyledon are called monocotyledonous or monocots. Plants with seeds having two cotyledons are called dicots.

Summary

• Eichler classified the plant kingdom into two sub-kingdoms Cryptogamae and Phanerogamae.
• Cryptogamaeincludes plants with hidden reproductive organs and plants do not bear flowers or seeds
• Thallophyta are the simplest of plants that do not have a well-differentiated body design.
• Algae do not have leaves, stems or roots.
• Bryophyta are often called amphibians of the plant kingdom.
• Plantae and Animalia are further divided into subdivisions on the basis of increasing complexity of body organisation.
• Plants are divided into five groups: Thallophytes, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms.