Classification of Kingdom Plantae (Metaphyta)
Classification of Kingdom Plantae
The study of plants is known as Phytology. Members of the kingdom Metaphyta (Plantae) are multicellular, eukaryotic, autotrophic organisms that contain chlorophyll, mainly chlorophyll a. Their cell walls are made up of cellulose and their growth is generally indefinite. The primary reserve food is starch, although in certain cases, fats are also stored. Being one of the most diverse kingdoms, plants have been classified by many botanists using different criteria such as reproductive structures, presence of seeds, and level of differentiation.
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Cell wall: cellulosic
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Growth: indefinite
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Reserve food: mainly starch (sometimes fat)
🔎 Historical Classifications
1. Eichler’s Classification (1883)
Eichler divided the plant kingdom into two subkingdoms mainly on the basis of the presence or absence of seeds.
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Cryptogamae
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Phanerogamae
The first subkingdom is Cryptogamae (from the Greek cryptos = hidden, gamos = marriage). These are lower plants in which the reproductive organs are hidden. They do not produce seeds or flowers. The group includes-
- Thallophytes
- Bryophytes
- Pteridophytes
Classification of Kingdom Plantae (Metaphyta)
The second subkingdom is Phanerogamae (from the Greek phaneros = visible, gamos = marriage). These are higher plants in which the reproductive organs are clearly visible. They produce seeds, and this group includes-
- Gymnosperms
- Angiosperms.
2. Endlicher’s Classification (1836)
Endlicher proposed an early system of classification in which he divided plants into three groups. Protophyta included primitive plants like algae and lichens. Histerophyta included fungi, which lack chlorophyll and are heterotrophic. The third group was Cormophyta, which included plants that possess differentiated organs such as roots, stems, and leaves. This classification was a significant step because it recognized the structural complexity of higher plants.
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Protophyta → Algae and Lichens
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Histerophyta → Fungi
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Cormophyta → Plants with root, stem, and leaves
Protophyta vs Histerophyta, vs Cormophyta
| Feature | Protophyta | Histerophyta | Cormophyta |
|---|---|---|---|
| Main Members | Algae, Bacteria, Lichens, Slime molds | Fungi | Mosses, Ferns, Gymnosperms, Angiosperms |
| Mode of Nutrition | Mostly autotrophic (photosynthetic algae); some heterotrophic | Heterotrophic, saprophytic or parasitic | Autotrophic (photosynthesis) |
| Cell Wall Composition | Mainly cellulose (in algae) or LPS (in bacteria) | Chitin | Cellulose |
| Organization | Unicellular or simple multicellular thallus | Multicellular filamentous or mycelial | Complex multicellular with organs |
| Vascular Tissue | Absent | Absent | Present (except in Bryophytes) |
| Reproductive Structures | Simple, unicellular gametangia | Spores produced in sporangia; sexual reproduction by gametangia | Flowers, cones, archegonia, antheridia (well-organized) |
| Embryo Formation | Absent | Absent | Present, develops from zygote |
| Habitats | Mostly aquatic or moist places | Damp, dark terrestrial habitats | Wide range – terrestrial, aquatic, aerial |
| Examples | Chlamydomonas, Nostoc, Volvox | Yeast, Rhizopus, Mushroom | Pteris (fern), Pinus, Mango, Rose |
| Evolutionary Significance | Most primitive plant-like organisms, showing first step towards multicellularity | Derived from protists, represent early heterotrophic evolution | Most advanced group with true tissues, vascular system, and embryo protection |
3. Engler’s Classification (1886)
Engler’s system of classification further refined the grouping of plants. He divided the plant kingdom into Thallophyta and Embryophyta.
Thallophytes are plants with a simple, thallus-like body that shows no embryo formation after fertilization. In contrast, Embryophytes are plants where the zygote develops into a multicellular embryo, marking a higher degree of organization.
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Thallophyta → Plant body thallus-like; no embryo formation
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Embryophyta → Zygote develops into a multicellular embryo
| Feature | Thallophyta | Embryophyta |
|---|---|---|
| Definition | Group of simple, primitive plants without differentiation into root, stem, and leaves. | Group of higher plants where zygote develops into a multicellular embryo. |
| Body Organization | Thallus-like, not differentiated into organs. | Differentiated into root, stem, and leaves. |
| Vascular Tissue | Absent | Present (except in Bryophytes) |
| Reproduction | Simple reproductive structures, mostly unicellular gametangia. | Complex multicellular gametangia with protective layers. |
| Embryo Formation | Absent – zygote does not develop into embryo. | Present – zygote develops into a multicellular embryo. |
| Examples | Algae, Fungi, Lichens (in earlier systems) | Bryophytes, Pteridophytes, Gymnosperms, Angiosperms |
| Evolutionary Status | Primitive plants in classification. | Advanced plants with well-developed structures. |
🌿 Thallophyta
The term Thallophyta comes from the Greek words thallos (undifferentiated) and phyton (plant). It was first introduced by Endlicher (1836). Later, Unger (1838) placed algae, fungi, and lichens under this group. However, in modern systems of classification, such as that of Whittaker (1969), fungi, bacteria, and lichens were excluded and placed in separate kingdoms due to their fundamental differences.
Thallophytes represent the simplest group of plants. They are seedless, flowerless, and non-vascular. Their plant body is called a thallus, which is usually haploid and gametophytic in nature. The body does not show true differentiation into root, stem, or leaves, and vascular tissues are entirely absent.
The reproductive structures of thallophytes are also very simple. The sex organs are usually unicellular, known as gametangia, and they are not covered or protected by sterile cells. In cases where the sex organs are multicellular, all the cells are fertile. After fertilization, the zygote is formed but it never develops into an embryo. Asexual reproduction often occurs through mitospores, and in many cases, the plant body is just one cell thick, without stomata. The process of meiosis is mainly zygotic, which means it occurs in the zygote. Altogether, thallophytes form a very large group, consisting of around two lakh (200,000) species.
General Characteristics of thallophytes-
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Simplest, seedless, flowerless, non-vascular plants.
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Plant body is thallus (haploid n, gametophytic).
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No differentiation into roots, stems, or leaves.
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Vascular system absent.
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Sex organs: unicellular (gametangia), not jacketed by sterile cells.
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If multicellular, all cells are fertile.
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Zygote does not develop into embryo.
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Asexual reproduction by mitospores.
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Body often one-celled in thickness and without stomata.
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Meiosis is mainly zygotic type.
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About 2,00,000 species belong to this group.
🌳 Cryptogamae and Phanerogamae
From Eichler’s classification, plants are broadly divided into two groups: Cryptogamae and Phanerogamae.
Cryptogamae are the lower plants, which include Thallophytes, Bryophytes, and Pteridophytes. They do not produce seeds, and their reproductive organs remain hidden. On the other hand, Phanerogamae are the higher plants, consisting of Gymnosperms and Angiosperms. These plants bear visible reproductive organs and produce seeds, which represent a major advancement in plant evolution.
Cryptogamae vs Phanerogamae
| Feature | Cryptogamae | Phanerogamae |
|---|---|---|
| Meaning | Plants with hidden reproductive organs | Plants with visible reproductive organs |
| Seeds | Absent | Present |
| Flowers | Absent | Present (in Angiosperms) |
| Reproductive organs | Simple, often unicellular, not externally visible | Complex, multicellular, externally visible |
| Groups included | Thallophytes, Bryophytes, Pteridophytes | Gymnosperms, Angiosperms |
| Evolutionary status | Lower plants | Higher plants |
| Embryo formation | Absent or very simple | Well-developed embryo after fertilization |
| Examples | Algae, Mosses, Ferns | Pines, Mango, Rose, Wheat |
Classification of Kingdom Plantae (Metaphyta)
The Plant Kingdom: A Comprehensive Overview – Alisciences
✨ Conclusion
The classification of the plant kingdom has evolved over time as botanists have tried to arrange plants based on their structure, reproduction, and level of differentiation. Starting from the early systems of Endlicher and Eichler to the later refinements by Engler, these classifications highlight the diversity and complexity of the plant kingdom. The study of thallophytes and other groups not only gives insight into the simpler forms of plants but also helps us understand the evolutionary transition towards higher plants such as gymnosperms and angiosperms.
Classification of Kingdom Plantae or Metaphyta
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