What are Plants?

Plants are part of the PLANT KINGDOM, which is one of the five kingdoms of life. Plants are divided into smaller classes based on common characteristics. Certain characteristics are shared by all plants. They are made up of a large number of cells. They also make their own food through a chemical process called photosynthesis, which involves the use of water, carbon dioxide, and solar energy. They pump life-giving oxygen into the air as a by-product.

Plants are multicellular species that are mostly photosynthetic eukaryotes in the Plantae kingdom. Plants were traditionally classified as one of two kingdoms, one of which included all non-animal living creatures, and the other of which included algae and fungi.

Characteristics of Kingdom Plantae

The plant kingdom has the following characteristic features:

1. They are non-motile.
2. Autotrophs are organisms that produce their own food.
3. They reproduce sexually or asexually by vegetative propagation.
4. Eukaryotes are multicellular organisms. The outer cell wall and a broad central vacuole make up the plant cell.
5. The plastids of plants produce photosynthetic pigments called chlorophyll.
6. For anchorage, reproduction, protection, and photosynthesis, they have different organelles.

Why are Plants Classified?

Based on their characteristics, all living species in the ecosystem are divided into kingdoms and sub-kingdoms. Plants, too, are divided into sub-kingdoms based on some distinguishing characteristics.

Plants are classified based on a variety of factors,

1. Botanical classification
2. Communities based on geography or ecology

Classification of Plants

According to the above-mentioned criteria, the plant kingdom has been divided into five subgroups:

• Thallophyta is a genus of plants.
• Bryophyta is a phylum of plants.
• Pteridophyta is a phylum of plants.
• Gymnosperms are a type of plant.
• Angiosperms are a type of flowering plant.

Thallophyta

Algae, fungi, and lichens with a poorly differentiated body shape are included in this division of the plant kingdom.

Characteristics of algae:

1. Algae are self-sustaining species.
2. They are known as thallus because their plant bodies are not divided into root, stem, and leaf.
3. Aquatic habitat, i.e., freshwater or sea water, is home to the majority of these species.
4. In wet soil, only a few algae can survive.
5. A number of them are very small and float on the water's surface. Phytoplankton is the name given to this type of algae.
6. Some lichens, including lichens, are symbiotic in nature, forming associations with fungi for mutual gain.
7. A few of them are epiphytes, meaning they grow on the plant's surface. Moisture and nutrients are obtained from the air, rain, and water surrounding the plant.

Bryophytes

These are the most primitive and basic plants, since they are non-vascular (they lack xylem and phloem) and seedless. As a result, they are referred to as vascular cryptogams. Water is needed for these plants to complete their life cycle, so they live on both land and water. As a result, they are known as the plant kingdom's amphibians.

Classification of bryophytes:

Bryophytes are classified into three classes as follows:

• Hepaticae (Liverworts)
• Anthoceratae (Hornworts)
• Musci (Mosses)

• Hepaticae (Liverworts):
  • They are plants that are closely related to the ancestor that migrated to land and are therefore of terrestrial habitat; they are the lower type of bryophytes since their structures are simpler than mosses.
  • Sporophyte is a simple, short-lived plant.

• Anthoceratae (Hornworts):
  • These are land plants that have colonised a variety of environments, but they are never far from a source of moisture.
  • These plants' gametophytes have an undifferentiated thallus and unicellular, unbranched rhizoids.
  • There is no protonemal stage (the first stage that grows directly from the spore).
  • Only the foot and capsule of the sporophyte are distinguished.

• Musci (Mosses):
  • Musci (Mosses) are bryophytes that exist in a wide range of habitats.
  • These are bryophytes with distinct gametophytes that include stems, leaves, and root-like sections.
  • There is a protonemal point.
    There are three types of sporophytes: foot, seta, and capsule.

Pteridophytes

The first land plants with vascular tissues are these (xylem and phloem). These vascular plants are classified as vascular cryptogams because they do not contain flowers or seeds. These plants are the most common and visible group of land plants, accounting for more than 90% of all vegetation on the planet.

True roots, branches, and leaves are well-differentiated in the plant body of these species.

Classification of pteridophytes:

The Pteridophytes are classified into four classes as follows:

• Psilopsida
• Lycopsida
• Sphenopsida
• Pteropsida

• Psilopsida: The most primitive pteridophytes are these. Rhizoids are present, but no leaves are present. These plants have homosporous sporophytes.

• Lycopsida: Club moss is the common name for these species. They have a plant body that is well-differentiated, with adventitious roots, stems, rhizophores, and leaves. Both homosporous and heterosporous sporophytes exist.

• Sphenopsida: Horsetails are the common name for them. Roots emerge from nodes of the underground rhizome, stem, and scaly leaves on these plants, which have a well-differentiated plant body. They're all the same.

• Pteropsida: The common name for them is horsetails. On these plants with a well-differentiated plant body, roots emerge from nodes of the underground rhizome, stem, and scaly leaves. They're all alike.

Gymnosperms

There are plants that grow seeds that are not contained within the ovary.

Characteristics of gymnosperms:

1. They can only be found in colder climates.
2. Gymnosperms are woody terrestrial plants with needle-like leaves.
3. The xylem lacks vessels, while the phloem lacks companion cells and sieve tubes.
4. While the male gametophyte produces two gametes, only one is functional.

Classification of gymnosperms:

Gymnosperms are classified into four different classes as follows:

• Cycadales
• Ginkgoales
• Coniferales
• Gnetales

• Cycadales: These are the upright, unbranched plants that look like palms. The tropics and subtropics are where they are most commonly found. These plants have pinnately compound leaves that form a crown. Taproots and coralloid are their roots.

• Ginkgoales: The large size and fan-shaped leaves of these plants distinguish them. The only living species in the group is Ginkgo biloba. All of the others have died out. This plant emits an unpleasant odour.

• Coniferales: These are the most well-known gymnosperm species. They are evergreen trees that look like cones. As a result, they don't shed in the winter. Their leaves resemble needles or scales. These plants have winged seeds that are produced in female cones.

• Gnetales: Angiosperms are a small group of plants that have advanced characteristics. Their flowery, soft-coated leaves are their most distinguishing feature. Their ovules are bare, just like the others, but they grow on a flower-like shoot.

Angiosperms: ngiosperms is derived from the Greek words “angio”, which means "covered," and sperma, which means "bean." Flowering plants are what they're called. The flowers that the plants grow develop into fruits, which contain seeds.

Classification of angiosperms: Cotyledons, or seed leaves, are structures found within the embryos of angiosperm seeds. During seed germination, these structures are usually green in color. Angiosperms are classified into two groups based on the number of cotyledons present in the seeds, that is, dicotyledons and monocotyledons.

Life Cycle of Plants

• The plant begins as a seed that germinates and develops into a full-fledged plant.
• Flowers are produced by the mature plant, which are fertilized and contain seeds in the form of a fruit or seedpod.
• When a plant dies, seeds are left behind, which germinate and develop into new plants.
• The life cycle of an annual is one year long.
• Biennials have a two-year life cycle, with the first year seeing them germinate and grow roots and leaves, followed by the second year seeing them bloom, set seed, and die.
• After germination, perennials live for many years.
• Monocarpic plants only produce seeds once, but they can take many years to mature. The Talpiot Palm will live for 60 years or more before flowering and producing seeds, after which it dies.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for

• Bachelors in Biology
• Bachelors. in Botany
• Masters in Botany

Related Concepts:

Lifecycle of animals and plants