R.H. Whittaker organized the organisms into five kingdoms. He classified organisms on the basis of cell structure, mode, the source of nutrition and body design. The five kingdoms proposed by Whittaker are Monera, Protista, Fungi, Plantae, and Animalia. Let’s learn about the plant kingdom i.e., kingdom Plantae.
Plant Kingdom – Plantae
Kingdom Plantae includes all the plants on the earth. They are multicellular, eukaryotes and consist of a rigid structure that surrounds the cell membrane called the cell wall. Plants also have a green coloured pigment called chlorophyll that is quite important for photosynthesis.
Characteristics of Kindom Plantae
The plant kingdom has the following characteristic features:
- They are non-motile.
- They usually reproduce sexually.
- They follow the autotrophic mode of nutrition.
- These are multicellular eukaryotes with cell wall and vacuoles.
- These contain photosynthetic pigments called chlorophyll in the plastids.
- They ave different organelles for anchorage, reproduction, support and photosynthesis.
Classification of Kingdom Plantae
A plant kingdom is a vast group; therefore, the kingdom is further classified into subgroups. Levels of classification are based on the following three criteria:
- Plant body: whether the body has well-differentiated structures or not.
- Vascular system: whether the plant has a vascular system for the transportation of substances or not
- Seed formation: whether the plant bears flowers and seeds or not; if it does, then whether it is enclosed within fruits or not.
Considering all these factors, the plant kingdom has been classified into five subgroups. They are as follows:
- Thallophyta
- Bryophyta
- Pteridophyta
- Gymnosperms
- Angiosperms
Thallophyta
All the plants that lack a well-differentiated body structure belong to the subgroup Thallophyta.
Thallophytes: Primitive plants where the body is not differentiated into stem, roots and leaves
Thallophytes commonly include members with primitive and simple body designs such as green algae and brown algae. The majority of them are aquatic. Common examples are Spirogyra, Chara, Ulothrix, etc.
Bryophyta
Bryophytes: Small, non-vascular plants that prefer moist environments
Bryophytes have differentiated plant body like stem, leaf structures. But they lack a vascular system for the transportation of substances across the plant body. Bryophytes are found in both land and aquatic habitats, hence are known as amphibians of the plant kingdom. Mosses and Marchantia belong to this subgroup.
Pteridophyta
Pteridophytes have well-differentiated structures such as stem, root, leaves as well as a vascular system.
Pteridophytes: Spore-dispersing vascular plants
Ferns, horsetails, Marsilea are some common examples of Pteridophytes.
Gymnosperms
Gymnosperms: Vascular plants that possess “exposed” seeds
Gymnosperms are plants that have well-differentiated plant body, vascular system and they bear seeds. The term is derived from Greek words, gymno: naked and sperma: seed. The seeds of gymnosperms are naked which means they are not enclosed within a fruit. The perennial, evergreen woody trees belong to this group. Pines, deodar, redwood, etc. are a few examples.
Angiosperms
Angiosperms: Vascular plants that possess special characteristics such as flowers and fruits
Angiosperms are also seed-bearing plants with well-differentiated plant body. The word is derived from Greek words: angio: covered and sperma: seed. Unlike gymnosperms, seeds of angiosperms are enclosed inside the fruits. Angiosperms are commonly known as flowering plants. Examples include the Mango tree, pomegranate plant, etc. Seeds germinate from embryonic leaves called cotyledons.
Depending on the number of cotyledons present in seeds, angiosperms are divided into two: monocotyledons or monocots and dicotyledons or dicots.
Cryptogams and PhAnerogams
The plant kingdom has also been classified into two groups ‘cryptogams’ and ‘phanerogams’ based on their seed formation ability.
Cryptogams are plants that do not have well-developed or conspicuous reproductive organs. They have hidden reproductive organs and don’t produce seeds. The thallophytes, the bryophytes and the pteridophytes are ‘cryptogams’. Reproduction in all three groups occurs through spore formation.
Plants that have conspicuous reproductive organs and produce seeds are called phanerogams. Gymnosperms and Angiosperms belong to the group phanerogams..
Frequently Asked Questions
Name the pigment responsible for photosynthesis in plants.
Chlorophyll is the pigment responsible for photosynthesis in plants.
Describe the criteria for levels of classification in plants.
Plants are classified into their respective classes based on the following three criteria:
- Plant body
- Vascular system
- Seed formation
Explain the characteristic of thallophytes.
Members of this class lack a well-differentiated body structure, or in other words, the body is not clearly divided into stem, leaves and roots.
Explain the significant features of Gymnosperms.
Gymnosperms include plants that possess a vascular system and a well-differentiated body structure. Furthermore, they bear seeds like the angiosperms, but they are not encased within a fruit. Hence, the term “Gymnosperm”, which is derived from Greek word, gymno = naked and Sperma = seed.
List the characteristics of Angiosperms
- Seed-bearing plants
- Seeds are enclosed within fruits
- Presence of well-differentiated plant body
- Produces flowers during their lifespan
- Presence of two subtypes – monocots and dicots
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