Plant Kingdom - Definition, Classifications and Characteristics
Plantae is the plant kingdom which contains all plants on the earth. They are multicellular eukaryotes. Characteristically, they contain a rigid structure that surrounds the cell membrane known as the cell wall. Plants also have a green colored pigment known as chlorophyll that is quite vital for photosynthesis. Hence, they have an autotrophic mode of nutrition. A plant kingdom is a massive group; hence, the kingdom is further categorized into subgroups. The best way to study about plants is to first recognize how the classification takes place within Kingdom Plantae. Once you know the simple stuff, it then becomes easier to be familiar with in detail about each plant.
Biologist Whittaker provided us the Five Kingdom Grouping, categorizing all the living organisms into five territories – Protista, Monera, Fungi, Plantae, and Animalia. To know additional about plants, it is vital to know more about the Kingdom Plantae or in simple versus the plant kingdom.
You will be astonished to see the different types of plants that are comprised here. You can see minute plants like the algae as well as the tallest vegetation like the Sequoia. Certain plants have the supremely beautiful and attractive looking organelles called flowers, while some don’t contain any. In certain plants, you can see an appropriate root system, shoot system, and leaves, while in the simpler plants, it is only a thalloid structure.
Level of classification is grounded on the following three criteria:
1. Plant body: whether the body has well-differentiated assemblies or not. 2. Vascular system: whether the plant has a vascular system for carrying of substances or not. 3. Seed development: whether the plant allows flowers and seeds or not; if it does, then whether it is surrounded by fruits or not.
Each group of plants has distinct and unique features that fit exclusively to that group. While the thallophytes are the greenest of the plants, the angiosperms are plants with a complex assembly and a very well-established vascular system and reproductive system.
The gymnosperms are the cluster of plants that have an evolutionary meaning. These are the first plants to have advanced seeds, which is a well-organized mechanism of continuing the plant group at places away from the parental plant.
Considering all these features, the plant kingdom has been separated into five subgroups. They are as follows:
All the plants that have short and well-differentiated bodybuilding belong to the subcategory Thallophyta. Thallophytes are generally known as algae. The popularity of them is water-based. Certain examples are Spirogyra, Chara, Ulothrix, etc.
Characteristics of Thallophyta
1. They are usually originated in moist or wet places.
2. This is due to the nonappearance of “true roots” and vascular tissue that is required to transport water and minerals. Therefore, they are found in moist or wet places.
3. They are autotrophic by nature.
4. Maximum members in this group produce their own food. But certain members like fungi are dependent on other sources of food.,
5. Reserve food is normally starch.
6. After the photosynthesis process, glucose is formed and consumed almost immediately, the remaining glucose is transformed into complex compounds called starch.
7. They contain a cell wall made up of cellulose around their cells.
8. Nonappearance of vascular tissue.
9. Unlike other plants, xylem and phloem are lacking. etc
10. Sex organs are simple, single-celled, there is no embryo making after fertilization.
Division of Thallophyta:
The separation Thallophyta is classified into two parts: Algae and Fungi.
They are chlorophyll-containing thalloids. They are autotrophic and largely water plants. On a side note, it has been seen that green algae procedures a symbiotic relationship with sloths that are natural to the lush tropical rainforests of South America and Central America. Sloth fur is very rough and readily absorbs water. As a result, sloth fur procedures are a moist and damp environment for the algae to flourish. The algae in return, deliver the sloth with extra nutrition and disguise from predators. Example: Spirogyra.
They are achlorophyllous (meaning they do not create chlorophyll) heterotrophic thallophytes. Occasionally, to overcome this handicap, fungi may grow a symbiotic relationship with algae or a cyanobacterium. The algae can create food as it has chlorophyll and the fungi in return offer a safe environment that shields the algae from Ultraviolet rays. Lichen is an example where two creatures act as a single part.
Bryophytes have distinguished plant body like leaf structures, stem. But they lack a vascular arrangement for the carrying substances through the plant body. Bryophytes originate in both land and aquatic environments, therefore are called amphibians of the plant kingdom. Mosses and Marchantia fit to this subcategory.
The only major feature of a bryophyte is that it does not have true vascular matter. Some do have tissues which are used to carrying water but are not considered to be a true vascular tissue due to the shortage of lignin. Bryophytes are believed to develop from charophytes and are considered to have been the first true plants ever developed.
Characteristics of Bryophytes
• Plants in this group do not have roots but contain crude stems and leaves. • They contain “rhizoids” in its place of roots which helps the plant to anchor to surface. • These roots do not absorb nutrients like other typical plant roots. • Mosses release spores from their leaves which passes by water and create new mosses in new sites. • Water is very vital for mosses to grow and spread. They can completely dry out and survive. When in touching base with water, then again wake up and continue growing.
The life cycle of Bryophytes is like all the other terrestrial plants (embryophytes) with the change of generations. A haploid gametophyte cell has a fixed number of unpaired chromosomes. It gives growth to diploid sporophyte, which however has twice the number of paired chromosomes. Diploid zygotes made by the fusion of haploid sperm and eggs formed by gametophytes. Diploid zygotes produce into a sporophyte.
Pteridophytes have well-distinguished structures such as stem, root, leaves as well as vascular tissue. Ferns, horsetails, Marsilea are some collective examples of Pteridophytes.
1. Psilotidae: Ophioglossales (example. grape ferns) and Psilotales. 2. Equisetidae (horsetails) 3. Polypodiidae (the most species-rich group, leptosporangiate ferns) 4. Marattiidae (marattioid ferns)
• Pteridophytes are the first true terrestrial plants: It is guessed that life began in the oceans, and through millions of years of development, life slowly adapted on to dry land (terrestrial). And among the first of the plants to truly live on terrestrial were the Pteridophytes. • They are plants which are seedless, vascular cryptogams: Pteridophytes are seedless and they produce through spores. They don't have to conduct tissues for carrying of water and minerals. In its place, the water and minerals run from the surface of the plant- cell to cell in the plant's body. This is also one of the explanations of why these plants need a continuously moist environment to live. • They show a true change of generations: The sporophyte group and the gametophyte group are observed in Pteridophytes. • Sporophyte has true roots, leaves, and stem. • Spores advanced in sporangia are homosporous: Sporangium is the assemblies in which spores are made. They are typically homosporous (importance: one type of spore is formed) and are also heterosporous, (meaning: two kinds of spores are formed.) • Sporangia are formed in groups on sporophylls: Leaves that tolerate the sporangia are named as sporophylls. • Young leaves of sporophyte display circinate vernation: The tip of the leaves tends to twist inwards to defend the vulnerable growing parts. • Sex organs multicellular and jacketed: The male sex organs are named antheridia while the female sex organs are termed archegonia.
Gymnosperms are plants that have well-distinguished plant body, vascular structure and they bear seeds. The name is derived from Greek words, gymno means naked and spermac means seed. The seeds of gymnosperms are naked which means they are not walled within a fruit. The constant, evergreen woody trees belong to this cluster. Pines, deodar, redwood, etc. are a few good
Features of Gymnosperms
Gymnosperms have an evolutionary meaning and show some sole features. Their distinguishing feature is the absence of flowers and occurrence of naked, open seeds. As they do not contain flowers, thus, fruits are also lacking in these cluster of plants.
The chief source of self-pollination and dispersal is wind. These are usually medium to tall trees, with a few shrub classes also present. Sequoia is a gymnosperm which is one of the biggest and tallest tree species.
The plant body displays differentiation and is separated into leaves, stem, and roots. The leaves are usually needle-like with a thick cuticle and sunken stomata, normally seen in conifers. This feature supports a decrease in water loss due to transpiration.
The root system existing in the gymnosperms is a taproot system. In certain plants, these roots have an association with fungi and form mycorrhiza, one example is Pinus. In a small number of extra species like the Cycas plant, the roots are in the form of specialized roots named coralloid roots and are related with nitrogen-fixing cyanobacteria. These plants are also vascular, with both xylem and phloem being existent.
Angiosperms are also seed-containing plants with well-distinguished plant body. The term is derived from Greek words: angio: enclosed and sperma: seed. Unlike gymnosperms, seeds of angiosperms are covered inside the fruits. Angiosperms are usually known as flowering plants. For instance, it contains the Mango tree, pomegranate plant, etc. Seeds develop from embryonic leaves named cotyledons.
Depending on the number of cotyledons existing in seeds, angiosperms are separated into two: monocotyledons (monocots) and dicotyledons (dicots.)
All angiosperm plants have the typical vascular bundle with the xylem and phloem materials for conduction of water, minerals, and nutrients. The plant body is well distinguished with a well-built root system, shoot system, and leaves. Particular structures called as the flowers are present. Within these flowers, the male and female gametes mature. After pollination, when these flowers developed, fruits are made which have the seeds within them.
Angiosperms can be seen in varied habitats and can come in a different variety of sizes. Wolfie is an angiosperm that is tiny whereas the Australian mountain ash tree is about 100 meters in height. The variety that the angiosperms have seen are very wide. There are several plants that are very tall woody trees, shrubs, and even herbaceous plants. These plants also have numerous adaptations in the roots, stems and leaves subject on the habitat that they raise in.
Classification of Angiosperms
Based on the types of cotyledon existing, angiosperms are separated into two classes. They are monocotyledons and dicotyledons. The dicotyledonous angiosperms have 2 cotyledons in their seeds and the monocotyledonous angiosperms contain 1 cotyledon.
The monocots have some different features that contain the occurrence of adventitious roots, simple leaves with similar venation, and trimerous flowers. The quantity of vascular bundles is more and is closed. Some of the examples contain bamboos, banana, sugarcane plants, cereals, lilies etc.
The dicotyledonous plants have two (2) cotyledons with a taproot arrangement. The venation observed in the leaves is reticulate. Flowers can be tetramerous or pentamerous. Vascular bundles are usually arranged in a ring and number between 2-6. Examples include Grapes, Sunflower, Tomatoes, Dandelions, and Potatoes.
Cryptogams and Phanerogams
The plant kingdom has been categorized into two groups ‘cryptogams’ and ‘phanerogams’ based on their seed development ability.
Cryptogams are plants that do not have well-built or visible reproductive organs. They have hidden reproductive organs and don't create seeds. The thallophytes, the bryophytes, and the pteridophytes are cryptogams. Reproductions in all the three individuals take place through spore formation.
Plants that have visible reproductive organs, can produced seeds are called ‘phanerogams’. Gymnosperms and Angiosperms have its place to the group phanerogams.