You hardly look at plants that do not bear flowers. Do you? It is obvious that fruits and flowers make a plant or tree very attractive. Are you aware that there are numerous types of plants based ONLY on the type of flowers and fruits that they have? We will look at the classification of flowering plants or angiosperms in this topic. Let’s begin.
What are Angiosperms?
In the angiosperms or flowering plants, the pollen grains and ovules are developed in specialised structures called flowers. In angiosperms, fruits enclose and protect the seeds. The angiosperms are a huge group of plants. They usually occur in a wide range of habitats. Their size ranges from tiny, almost microscopic Wolfia to tall trees of Eucalyptus (over 100 metres).
They are the plants that provide us with food, fodder, fuel, medicines and several other commercially important products. We can divide them into two classes: the dicotyledons and the monocotyledons. The dicotyledons are those that have two cotyledons in their seeds. On the other hand, the monocotyledons have only one. Let us now look at the classification of flowering plants in more details.
Classification of Flowering Plants
The classification of flowering plants is done into two major groups: Dicotyledons and Monocotyledons.
They show the following distinguishing characteristics:
- They have tap roots.
- The leaves in members of these class exhibit reticulate (net-like) venation.
- The flowers are tetramerous or pentamerous. They have four or five members in the various floral whorls, respectively.
- The vascular bundles in these plants are arranged in a ring. They are numbered 2-6, are open and with cambium.
- The seeds of dicotyledons are with two cotyledons, as we already know from the name.
They show the following characteristics:
- They have adventitious roots.
- The leaves are simple with parallel venation.
- The flowers are trimerous having three members in each floral whorl.
- The vascular bundles are scattered in the ground tissue, are many in number and without cambium.
- The seeds of monocotyledons are with one cotyledon as the name indicates. Examples include Cereals, bamboos, sugarcane, palms, banana, lilies and orchids.
Based on Longevity
We can divide flowering plants into 4 types based on the duration of their life. They are:
- Ephemerals: This category of plants can only live for a few weeks. This is mainly because they have a very short growing season. We find such plants near deserts or in very cold countries. For example, Arabidopsis species have a lifespan of 20–28 days.
- Annuals: These plants live and complete their life-cycle in a single favourable season. During this period, they grow in size and produce flowers. These plants also shed their seeds, undergo senescence and die in this phase. They pass the unfavourable period in the form of seeds. Many crop plants (e.g., wheat, rice, maize, etc.) are annuals. The smallest angiosperm – Wolffia is an aquatic annual.
- Biennials: These plants are known to complete their life-cycle in two favourable seasons (i.e., in two years). They grow vegetatively in the first season. On the other hand, these produce flowers and set seeds in the next. Often they produce some storage organs, as in the sugar beet, where food is stored in their swollen roots.
- Perennials: These plants can live for more than two years. Generally, they live for many years and bear the flowers and fruits during specific seasons. Some of these perennials can continue their vegetative growth for several years. They produce fruits and seeds only once in their lifetime. Examples include Agave, Bamboos, etc. They are monocarpic.
Based on the Habit of Plants
Angiosperms belong to following categories on the basis of their habits:
- Herb: Herbs are small, soft, non-woody plants. They do not have persistent parts above the ground. The height of plants usually reaches up to 1 m. The plants may be annual (Brassica), biennial (Sugar beet) or perennial (Canna).
- Shrubs: These are of a relatively lower height and are woody plants. their height can vary from 1-4 m. They typically branch at or near the base and do not have the main trunk, e.g., Rose. They are mostly perennial.
- Trees: These are perennial woody plants with one main trunk. The trunk may or may not be branched.
Solved Example for You
Q: Classify plants on the basis of their habitat.
Ans: We can divide plants into four major groups – hydrophytes, mesophytes, xerophytes and halophytes. This classification is on the basis of their habitat. We can also include a fifth group, epiphytes.
(i) Hydrophytes: The plants which grow in aquatic habitats are called hydrophytes. We can further group them as–
- Submerged (e.g., Hydrilla)
- Attached floating (e.g., Nymphaea)
- Free-floating (e.g., Eichhornia, Wolffa)
- Amphibious or partly emerged hydrophytes (e.g., Sagittaria).
(ii) Mesophytes: These plants grow under moderate moisture and temperature conditions. They are not usually adapted to grow either in very dry or in very wet conditions (e.g., Sunflower, Brassica). These plants do not possess special adaptations to reduce transpiration.
(iii) Xerophytes: These plants grow in dry or xeric habitats (i.e., under deficient supply to available water). They face acute shortage of water. This is the reason they develop morphological, structural and physiological adaptations as a weapon to survive under such habitats.
(iv) Halophytes: Halophytes are those plants which grow in saline habitats, i.e., in salt marshes, alkaline soils, river estuaries, saline ponds near seashore or sandy and heavy soils having an excess of salts. In such habitats, the water is present in sufficient amount but due to high osmotic concentrations, it is physiologically not available to normal plants. Such conditions are physiologically dry. e.g., Spartina, Atriplex, Portulaca etc.
(v) Epiphytes: These are the plants which grow on other plants for space only. The plants are autotrophic and occur both in aquatic and terrestrial habitats. e.g., Vanda (an orchid).