Classification of Plants: Plant Kingdom

Plants are very complex and diverse, with millions of distinct species, some of which have yet to be completely identified and investigated. While all plants have identical elements that are necessary for their life, i.e., roots, stems, leaves, etc, they typically look different. Plants differ from one another in terms of appearance, structure, and physiological functioning. They also differ in terms of habitat, tolerance, and nutritional requirements. Botanists have previously established classification systems for plants. These distinctions in features are used to divide plants into species, which allows them to be classified and organised. Plant classification is, in reality, one of the oldest techniques of understanding botany.

Key Terms: Plants, Kingdom Plantae, Thallophyta, Pteridophyta, Coniferophyta, Bryophyta, Angiosperms, Monocotyledons, Dicotyledons, Annuals, Biennials, Perennials

Read More: Basic Internal Anatomy of Leaf

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Importance of Classification of Plants

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The primary goal of plant classification is to guarantee that the plants are named, categorised, and recognised properly. These three traits are used to classify plants:

• Woody plants are classified as either deciduous or evergreen.
• Plants that keep their leaves at all seasons are known as evergreens (all year round).
• Plants that lose their leaves at the end of the growing season, either during the winter season in temperate climates or during the dry season in tropical climates, are known as deciduous.

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Kingdom Plantae

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The kingdom Plantae encompasses all of the land plants. They are eukaryotic, multicellular, and autotrophic creatures. Plant cells have thick cell walls that protect them from hazardous substances. Chlorophyll pigment and chloroplast are held in photosynthesis by plants.

Kingdom Plantae

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Characteristics of Kingdom Plantae 

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The following are the features of the plant kingdom:

• They are immobile and spend their whole lives in one location.
• Autotrophs are plants that produce their own sustenance.
• Plants reproduce in two ways: vegetative propagation and sexual reproduction.
• Plants are multicellular eukaryotes because they have exterior cell walls and a big central vacuole that serves to store waste materials.
• Chlorophyll pigments are responsible for the green colour of plants and for photosynthesis.
• For reproduction, support, anchoring, and photosynthesis, plants contain distinct organelles.
• Plants exhibit generational change.
• Gametophyte and sporophyte are the two stages of plant life.

Read More: Fertilization in Plants

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Classification Based on Life Cycle

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Plants are categorised according to their life cycle.

• Annuals

These are plants that go through their whole life cycle in one season. Normally, they are herbaceous. Annual plants include corn, rice, wheat, and legumes, to name a few.

• Biennials

The life cycle of these plants takes two years to complete. Normally, they are herbaceous. Carrots, cabbage, onions, and beetroots, for example, are biennial plants.

• Perennials

These are plants that live for an extended period of time, usually more than two years. They have a woody or herbaceous appearance. Perennials include roses, lavender, dianthus, and lilies, to name a few.

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Taxonomic Classification of Plants

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Taxonomy is a classification system for plants based on their genetic and evolutionary connections. Plant taxonomy is a discipline of science that is constantly evolving as new species are discovered on a daily basis. Plants are divided into their own kingdom, the Kingdom Plantae. The present plant categorization system is based on evolutionary relationships between plants.

Read More: Double Fertilization in Angiosperms

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Cryptograms and Phanerogams

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Cryptograms are plants that do not produce flowers or, in other words, non-flowering plants. Thallophyta, Bryophyta, and Pteridophyta are the three divisions of cryptograms. Phanerogams produce flowers, and all flowering plants are classified as phanerogams, which are further separated into two groups: Gymnosperms and Angiosperms. The plant kingdom has been classified into five primary subgroups based on all of these criteria. They are as stated previously.

Cryptograms

Thallophyta

Thallophyta is a poorly divided phylum. Plant sections and body structures are not highly distinguished in them. They are devoid of real stems and roots. Thallophyta creatures are multicellular or eukaryotic, meaning they have well-defined cell membrane-bound organisms. They don't move around. They have various pigments. Algae are the name for these plants. They are primarily aquatic, as well as tasty and hazardous. Spirogyra, cladophora, and Ulva are examples.

Thallophyta

Bryophyta (Non-Vascular Plants)

The plant kingdom's amphibian is Bryophyta. The body is divided into two parts: stems and leaves. Rhizoids, which look like roots, are also found. They are obligate autotrophs. There is no specialised tissue for water and food conduction. They thrive in wet and moist environments.

• With over 10,000 plant species, the Phylum Bryophyta is the most diversified. Mosses, liverworts, and hornworts are all members of this phylum. The taxonomy of several bryophyte species is currently arbitrary, and more research is needed.
• The members of the Phylum Bryophyta are the most basic of all plant phyla. Mosses have a modest and unassuming physical appearance.
• Bryophytes are structurally weak because they lack vascular tissue and wood. They also lack genuine leaves, stalks, and roots, which would aid in the transportation of water and nutrients. As a result, they are restricted to a few environments.
• Despite the fact that they lack several vital plant parts, bryophytes perform a significant role in reducing erosion along waterways, carrying out water and nutrient cycling in forests, and controlling the temperature in permafrost. 
• Lichens and bryophytes have similar environments and physical features (symbiotic relationship between a fungus and algae). For example, both of them use environmental moisture to deliver minerals and nutrients.
• As a result, bryophytes prefer wet environments and have evolved many strategies to assist them to flourish during dry seasons. Bryophytes reproduce through spore production.

Bryophytes

Pteridophyta (Vascular Plants)

The first terrestrial plant is Pteridophyta. They have distinct plant bodies, which are divided into roots, leaves, and stems. Leaflets are the individual parts of a leaf. Sporophylls are spores that are carried by leaflets. Hidden are well-developed reproductive organs. There is specialised tissue for food and water conduction, i.e. vascular tissue. Found in rock fissures, wet, shaded areas. Marsilea and fern, for example.

• Pteridophytes are seedless plants, which means they can't transfer their genetic information to their progeny through cones, fruits, or seeds. Instead, this type of plant generates spores called sporophylls, which are found on the underside of the leaves.
• Because of the spring-like architecture of these sporangia-containing spores, Pteridophytes may catapult their spores even over large distances.
• Pteridophytes have a wide range of physical characteristics, and no single trait can adequately define them. The leaves of ferns are called fronds, and they are usually coiled until they mature. They also have simple leaf roots and horizontal stems called rhizomes. They are already vascular plants capable of transferring fluids, unlike bryophytes.
• Pteridophytes have evolved to a broad range of habitats over time: they may be aquatic, terrestrial, and even cold-resistant, yet they still favour tropical environments. 

Pteridophyta

Read More: Difference between bryophytes and pteridophytes

Coniferophyta (Gymnosperms)

Gymnosperm comes from the Greek term Gymno, which means "without cover." Sperma - seed, i.e. seeds that do not bear fruit. They are simple, basic seed plants. Perennials, evergreens, and most woody plants are typical. There are true roots, stems, and leaves. There are no xylem vessels. There are no phloem partner cells. It is a collection of mostly evergreen plants that are endemic to the temperate zone. So far, over 700 species have been found. They are non-flowering, vascular plants that generate seeds instead of flowers and fruits. Pines, cycads, cedars, and other gymnosperms are common examples.

• Pines, hemlocks, firs, and spruces are all members of this phylum, and they all have wood and green needle-like or scale-like leaves.
• Gymnosperm members demonstrate by reproducing using cones rather than seeds.
• Gymnosperms are heterosporous in nature. This indicates that the male and female cones are produced in different ways. Male cones are usually smaller than female cones, which are larger.
• Gymnosperms are excellent providers of wood and paper, as previously stated. Aside from that, they provide food and habitat for animals, who in turn play a vital role in the propagation of their propagules.

Gymnosperms

Read More: Difference Between Xylem And Phloem

Anthophyta (Angiosperms)

The name angiosperm comes from the Greek word angiosperma. Covered (Angio) & Seed (sperm).These are highly complicated plants with the most complicated reproductive system. They generated seeds that were encased in the fruit. These plants are blooming, which implies they produce flowers. The ovary is where seeds form. The ovary is transformed into a fruit. Embryos are found inside seeds. 

Angiosperms are enormous and have extremely sophisticated tissue. They may become large trees, tiny shrubs, bushes, and plants. Angiosperms are found all over the planet. This section encompasses the majority of the plants we encounter. Angiosperms are distinguished by their entirely contained seeds in fruits. 

• Angiosperms are plants that include trees, herbs, shrubs, bulbs, epiphytes (parasitic plants), and plants that live in both marine and freshwater environments.
• The Orchidaceae (orchid family), Asteraceae (daisy family), and Fabaceae (fabric family) are the three major families in this phylum (family of legumes).
• Despite its variety, this phylum shares a number of common characteristics.
• ovules/seeds contained within the carpel/fruit.
• The process of twofold fertilisation leads to the production of the nutritive tissue known as endosperm.
• Two pairs of pollen sacs, among other things, make up male reproductive tissue. 
• The first known angiosperms were the magnoliids, a group of plants consisting of tiny, inconspicuous blooming plants.
• Monocots and eudicots are thought to have evolved from this group.
• Angiosperms have a wide range of use for animals, particularly humans, due to their diverse varieties. Food, medicine, clothing fibres, and timber can all be found in angiosperms.

Angiosperms

Angiosperms is divided into two parts:

• Monocotyledons: Monocotyledonous plants are more often known as monocots. They are blooming plants having one cotyledon in each seed. Their leaves have a parallel-veined venation pattern. Rice, corn, sugarcane, tulips, onion, and other monocot plants are frequent examples. 
• Dicotyledons: Plants that are dicotyledonous are referred to as dicots. They are flowering plants with two cotyledons that are commonly grown as herbs, shrubs, and trees. The leaves have a venation pattern that emanates from a central main vein. Figs, eucalyptus, potato, tomato, hibiscus, and other plants are frequent examples. 

Read More: Difference Between Dicotyledons and Monocotyledons

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Things to Remember

• The general classification of plants is basically done on certain criteria such as Botanical type and Geographical or ecological communities.
• Plants have been classified into a separate kingdom called the Kingdom Plantae.
• The kingdom Plantae covers all the land plants
• On the basis of their life cycle, plants can be classified into Annuals, Biennials and Perennials. 
• Cryptograms and Phanerogams, Thallophyta, Bryophyta, Pteridophyta, Coniferophyta, and Anthophyta are the various classifications of Kingdom Plantae. 
• Angiosperms have been further classified into Monocotyledons and Dicotyledons.

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