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'. Most of the plants also have a green-colored pigment called 'chlorophyll' that is quite important for photosynthesis.
In this lesson, we will discuss the classification of the plant kingdom into five subgroups - thallophyta, bryophyta, pteridophyta, gymnosperms, and angiosperms.
The plant kingdom has the following six characteristic features:
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, vascular system, and seed formation.
Based on all these factors, the plant kingdom has been classified into the following five subgroups.
Let's discuss each subgroup further.
Thallophytes (Greek words: thallos = young shoot and phyton = plant) are simple, autotrophic non-vascular plants that lack a well-differentiated body structure. These include members with primitive and simple body designs such as green algae and brown algae. Common examples are Spirogyra, Chara, Ulothrix, etc.
These grow in specialized habitats:
Bryophytes (Greek words: bryon = moss and phyton = plant) have a 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. They are most common in moist and shady places. Some bryophytes also grow in diverse habitats like extremely dry or watery habitats. They reproduce sexually. Antheridium is the male sex organs, and archegonium is the female sex organ. Mosses and Marchantia belong to this subgroup.
The pteridophytes (Greek words: pteron = feather and phyton = plants) refers to all those plants with feathers like fronds of ferns. They have well-differentiated structures such as stem, root, leaves as well as a vascular system. They do not have flowers or seeds. These plants are mostly terrestrial. They prefer shady habitats. Ferns, horsetails, Marsilea are some common examples of Pteridophytes.
Gymnosperms (Greek words: gymno = naked and sperma = seed) are plants that have a well-differentiated plant body, vascular system, and they bear seeds. The seeds of gymnosperms are naked which means that they are not enclosed within a fruit. The perennial, evergreen woody trees belong to this group. Pines, redwood, etc, are a few examples.
Angiosperms (Greek words: angio = covered and sperma = seed) are also seed-bearing plants with a well-differentiated plant body. Unlike gymnosperms, seeds of angiosperms are enclosed inside the fruits. Angiosperms are commonly known as flowering plants. Fruits, grains, vegetables, trees, shrubs, grasses, and flowers are angiosperms. Most of the plants that we eat today are angiosperms.
Seeds germinate from the embryonic leaves called cotyledons. Depending on the number of cotyledons present in seeds, angiosperms are divided into two: monocotyledons or monocots (one cotyledon), and dicotyledons or dicots (two cotyledons).
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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, producing seeds are called phanerogams. Gymnosperms and Angiosperms belong to the group phanerogams.
