Flower
Flowers are no doubt the most enticing parts of plants. You hardly even look at the plants who do not have flowers! Isn’t it? However, more than the aesthetic pleasure, the flower performs other important functions. Ever wondered if flower bouquet didn’t exist. Yes! Flowers are so much more than the beautiful and colorful petals and fragrance.
Here, we will study flowers in more detail. We will cover all of the various parts of flowers as well. But, before we proceed, do you know what flowers actually are?
What are Flowers?
Flowers are the reproductive unit in the angiosperms. These are the main parts responsible for sexual reproduction in these plants. In simple terms, without flowers, these angiosperms won’t be able to produce more like themselves! A typical flower has four different kinds of whorls arranged successively on the swollen end of the stalk or pedicel, called thalamus or receptacle.
These four parts are called calyx, corolla, androecium, and
gynoecium. Calyx and corolla are accessory organs. On the other
hand, androecium and gynoecium are reproductive organs. However, there are some exceptions to this.
Perianth
In some flowers like lily, the calyx and corolla are not distinct and are termed as perianth. Now, we will look at the various parts of flowers in greater details.
Parts of the Flower
Each flower normally has four floral whorls, viz., calyx, corolla, androecium, and gynoecium. Let us look at each of these parts individually.
i) Calyx (Sepals)
The calyx may be gamosepalous (sepals united) or polysepalous (sepals free). Generally, sepals are green, leaf-like and protect the flower in the bud stage. They form the outermost whorl of the flower.
ii) Corolla (Petals)
Petals are usually brightly coloured to attract insects for pollination. Yes! That is why the flowers are coloured and attractive! Corolla may be also free (gamopetalous) or united (polypetalous). The shape and colour of corolla vary greatly in plants. It may be tubular, bell-shaped, funnel-shaped or wheel-shaped.
iii) Androecium (Stamens)
This part of the flower represents the male reproductive organ. Each stamen consists of a stalk or a filament and an anther. Each anther is usually bilobed and each lobe has two chambers, the pollen-sacs. The pollen grains are produced in pollen-sacs. A staminode is a sterile stamen.
When stamens are attached to the petals, they are called epipetalous.
The examples of this type include brinjal. When stamens are attached to the perianth, they are called epiphyllous. Lily is an example of this
type. Flowers are also classified on the basis of the fusion of stamen.
They are divided into the following types.
● Polyandrous: In this, the stamens in a flower remain free.
● Monadelphous: In these, the stamens are united into one bundle. Examples include China rose.
● Diadelphous: These have the stamens united into two bundles.
Examples include pea.
● Polyadelphous: In Polyadelphous, the stamens are united into more than two bundles. Examples include citrus. There may be a variation in the length of filaments within a flower, as in Salvia and mustard.
iv) Gynoecium (Carpels/Pistils)
The gynoecium is the female reproductive part of the flower. It consists of three parts – stigma, style, and ovary. An ovary is the enlarged basal part, on which lies the elongated tube, the style. The style connects the ovary to the stigma. The stigma is usually at the tip of the style and is the receptive surface for pollen grains.
Each ovary bears one or more ovules attached to a flattened,
cushion-like placenta. We can classify gynoecium into further types:
● Monocarpellary: These have only one carpel.
● Multicarpellary: These have more than one carpel.
● Apocarpous: When carpels are free. e.g., lotus and rose.
● Syncarpous: When carpels are fused. e.g., mustard and tomato.
After fertilisation, the ovules develop into seeds and the ovary matures into a fruit.
Aestivation
Aestivation is the mode of arrangement of sepals or petals in the floral bud with respect to the other members of the same whorl. We have mentioned the various possibilities below.
● Valvate: When sepals or petals in a whorl just touch one another at the margin, without overlapping. e.g., Calotropis.
● Twisted: If one margin of the appendage overlaps that of the next one and so on. e.g., China rose, lady’s finger and cotton.
● Imbricate: If the margins of sepals or petals overlap one another but not in any particular direction. e.g., Cassia and gulmohur.
● Vexillary (papilionaceous): It’s a special type of aestivation. It has five petals, the largest (standard) overlaps the two lateral petals (wings) which in turn overlap the two smallest anterior petals (keel). e.g., Pea, Bean.
Solved Examples for You
Q: Mention the different types of flowers.
Solution: There are different types of flowers based on their reproductive organs, symmetry etc.
● On the basis of reproductive organs, flowers are unisexual or bisexual.
● On the basis of symmetry, flowers are Actinomorphic (radial symmetry), zygomorphic (bilateral symmetry) or asymmetric (irregular).
● A flower may be trimerous, tetramerous or pentamerous when the floral appendages are in multiple of 3, 4 or 5, respectively.
● On the basis of bracts, flowers can be Bracteate and Ebracteate.
Inflorescence
Have you ever wondered why some flowers bloom in bunches while some others bloom vertically? No, that is no magic! There is pure science behind it. As biology students, you must be aware of the term inflorescence. In this chapter, we will study more about inflorescence.
We will also look at the various inflorescence types in different categories.
What is Inflorescence?
Inflorescence is the arrangement of flowers on the floral axis. The flowers are arranged with respect to a fixed floral axis. We will look at the various types and arrangements of flowers now.
1) Racemose
In this type of inflorescence, the main axis continues to grow. It does not terminate in a flower and gives off flowers laterally in an acropetal
manner (where old flowers are arranged lower side and young flowers are on the upper side). We can further divide it into:
● Raceme: When peduncle or (main axis) is elongated and flowers are pedicellate. Eg. Radish, Mustard
● Spike: Here, the peduncle is elongated but flowers are sessile.
Eg.Achyranthes.
● Catkin/Amentum: Here, the peduncle is thin, long and weak.
The flowers are sessile and unisexual. Eg. Mulberry, Betula, Oak.
● Spadix: In it, the peduncle is thick, long and fleshy. The flowers are small, sessile and unisexual. Examples include Colocasia, Maize, Aroids, Palms etc.
● Corymb: In it, the peduncle is short and all flowers are present at the same level because the lower flower has much long
pedicel than the upper one. eg. Candytuft
● Umbel: An inflorescence in which the flower stalks are of more or less equal in length, arise from the same point. At the base of flowers stalk, there is a whorl of bracts forming the involucre.
Eg.Centella.
● Capitulum/Racemose head (Anthodium): Here, the peduncle doesn’t grow. It becomes broad, flattened concave or convex.
Learn more about the Types and Parts of Flower here in more detail.
2) Cymose
In this type of inflorescence, the peduncle terminates in a flower.
Here, the older flowers are present at the upper portion and young
buds are arranged towards the base. This arrangement is called as the basipetal succession. It is of the following types:
● Uniparous cyme/Monochasial cyme: The peduncle ends in a flower producing lateral branch at a time It is of two types again: Helicoid cyme and Scorpioid cyme.
● Dichasial or biparous cyme: In this type, peduncle ends in a flower and from the basal part of peduncle, two lateral
branches arise. These also end in a flower and this same arrangement occurs on these lateral branches. Eg.
Bougainvillaea, Jasmine, Teak, Mirabilis.
● Multiparous cyme/Polychasial: Here, the peduncle ends in a flower and from the base of it many lateral branches arise, which also terminate in flowers.
Now, we will look at some special types of Inflorescence.
Inflorescence Types
1) Cyathium
The bracts or the involucre fuse and form a cup-shaped structure on the margin. This houses the glands. In the central part of the
cup-shaped structure, you can find the female flowers. These mature earlier. Due to the growth of pedicel, this comes out from the
cup-shaped structure.
Small male flowers surround these female flowers. These are also found on Pedicel. The male flowers, which lie towards the centre, mature earlier than the flowers which are towards the periphery. This inflorescence is found in Euphorbiaceae family like Euphorbia,
Poinsettia, Pedilanthus.
2) Verticillaster
We can find this type of inflorescence in Labiatae/Lamiaceae family, where the leaves are arranged in opposite manner on the stem. From the axil of each leaf, inflorescence develops. From the main axil, lateral axil arises, on which flowers you can find the flowers.
Examples include Salvia, Ocimum, Coleus etc.
3) Hypanthium
In this type of inflorescence, you can see the peduncle modified in narrow cup-like structure. At the base of the cup, the female flowers develop while towards mouth the male flower develops. All three types of flowers are present in this inflorescence. Eg. Banyan, Peepal etc.
Solved Example for You
Question: Write a note on Mixed Inflorescence.
Solution: In this arrangement, you can find the flowers arranged in both racemose and cymose manner on the same peduncle. It is further of two types:
● Mixed spadix: eg: Banana
● Cymose raceme or thyrsus: eg: Grapes
Leaf
We all know what leaves are, don’t we? However, when we are a
student of biology, our knowledge has to be different from what others know. Do you agree? So, for you, Leaves are not the green parts of the plants that have chlorophyll in them. You are too old for that! In this chapter of plant morphology, we will look into greater depths of Leaves. We will look at their characteristics and types. However, before we proceed, let us first know what a leaf is!
What is a Leaf?
The leaf is a green, flat, thin, expanded lateral appendage of the stem.
This part is borne at a node and bears a bud in its axil. It is exogenous in origin and develops from the leaf primordium of shoot apex. The green colour of the leaf is due to the presence of the photosynthetic pigment – chlorophyll. This pigment helps the various plants to synthesise their organic food.
You must have heard of the term foliage. Foliage refers to the green photosynthetic leaves of a plant. They are borne on the stem in
acropetal succession. Now, we move on to the section where we look at the various characteristics of leaves.
Browse more Topics under Morphology Of Flowering Plants
● Flower
● Inflorescence
● Root
● Stem
● The Fruit
● The Seed
● Classification of Flowering Plant
Characteristics of a Leaf
● The leaf is a lateral dissimilar appendage of the stem.
● A leaf is always borne at the node of the stem.
● Generally, there is always an axillary bud in the axil of a leaf.
● It is exogenous in origin and develops from the swollen leaf primordium of the growing apex.
● The growth of leaf is limited.
● The leaves do not possess any apical bud or a regular growing point.
● A leaf has three main parts – Leaf base, petiole and leaf lamina.
In addition, it may possess two lateral outgrowths of the leaf base, called stipules.
● The leaf lamina is traversed by prominent vascular strands, called veins.
Venation
It is the arrangement of veins and also the various veinlets in the leaves. Different plants show different types of venation. Usually, there are two types of venation:
● Reticulate venation: In a reticulate venation, the veinlets are arranged in a random fashion to form a complex network of veinlets. Ex: Dicotyledonous plants like a rose plant.
● Parallel venation: In this fashion, the veinlets are arranged parallel to each other. Ex: In monocotyledons like paddy.
Types of Leaves
You have possibly come across various plants with different shapes and sizes of leaves. They are categorized as follows:
● Acicular type: They are needle-shaped.
● Linear Type: They are long and relatively broader as compared to other leaves.
● Lanceolate Type: They are lance-shaped.
● Oblong Type: They are rectangular in their shape and structure.
● Reniform type: They refer to the leaves with the shape of kidneys.
● Cordate type: They are heart-shaped and have a deep notch at the base.
● Orbicular type: They are more or less circular in their shape.
● Saggitate type: They are shaped like arrow-heads.
● Elliptical Type: They have shapes of ellipses.
● Hastate type: The shape of these leaves is like saggitate. The two basal lobes are directed outwards.
● Ovate Type: They are oval or egg-shaped in their structure.
● Lyrate Type: They are in the shape of a lyre.
● Spatulate Type: They have shapes resembling spatulas or spoons.
● Centric Type: They are cylindrical and hollow.
● Oblique Type: The lamina of this leaf has unequal halves.
● Cuneate Type: They are wedge-shaped.
This is all about the characteristics and types of leaves. We will look at a few solved examples for a better understanding.
Solved Examples for You
Question: Explain how various leaf modifications help plants.
Solution: Though the main function of leaves is to carry out
photosynthesis, in a lot of plants, the modification of roots performs
various functions. Therefore, they become an important part of the plants. They include
● Tendrils: These help the plant in climbing.
● Spines: These act as an organ of defence. The common example includes cactus.
Root
Have you ever wondered why various flowers are different in their looks, place of origin and season of growth? Why don’t you find your favourite marigold flowers in the scorching summers? Well, there is a lot of story behind it! In this chapter, we will discuss everything about roots. Ever thought that roots are that significant? Yes! Before, we proceed, we will have a quick recap of what morphology is all about
What is Morphology?
Morphology is the branch of science related to the study of form and structure of anything. In botany, it generally means the study of
external features, forms and relative positions of different organs on
plants. Angiosperms or flowering plants show a great variety of shape, size and form.
They could range from minute Wolffia and Lamna (0.1cm) to the tall Eucalyptus (up to 100 meters). Now we head on to read more about a significant part of the flowering plants: the roots.
The Roots
The root is usually an underground part of the plant. It is primarily responsible for the fixation and absorption of water. The root with its branches is known as the root system. Now, we move ahead and look at the characteristics of the roots in various plants.
Characteristics of the Root
● The root is the descending portion of the plant axis.
● It is positively geotropic.
● It is usually non-green or brown in colour.
● The root is not further differentiated into nodes and internodes.
● As per the rule, the root does not bear leaves and tree buds.
● Usually, a root cap protects the root tip.
● The root bears unicellular root hairs.
● Lateral roots arise from the root. These are endogenous in origin (arises from pericycle).
Without the roots, the transportation system in many plants would cease to exist. Therefore, it is important that you understand the need for roots. However, there are more than one types of root systems in plants. We will now look at them in brief.
Types of Root System
The root system is generally of two types. We will look at these two types in the section below.
● Taproot system: The taproot system develops from radicle of the germinating seed. It is also called the normal root system.
The taproot system is present in only dicotyledonous plants.
● Adventitious root system: The root system that develops from any part of the plant body other than the radicle is called the adventitious root system. It is mostly seen in
monocotyledonous plants.
Regions of the Root
● Root Cap: The root cap is a thimble-like structure covering the tip of the root. The root cap protects the tender root apex when it makes its way through the soil.
● Region of Elongation: This part is responsible for the
meristematic activity. The cells in this region are very small, have a thin wall and dense protoplasm.
● Region of Maturation: We get the root hairs in this region.
These are a part of the root epidermis.
Modifications of Root
● Food storage: Taproots of turnip and carrot are examples where roots are modified for food storage.
● Support: In banyan trees, hanging roots come out from branches. The hanging roots then go into the soil to provide additional support to the huge banyan tree.
● Respiration: In swampy plants, many roots come out vertically above the ground. These are hollow roots and their primary function is the exchange of gases in the roots.
Solved Examples for You
Question: Pneumatophores or breathing roots occur in
A. Hydrophytes B. Epiphytes C. Xerophytes D. Mangrove plants
Solution: Pneumatophores are respiratory roots belonging to Mangrove plants. Hence, the correct answer is option d.
Question: Haustoria or sucking roots occur in A. Betel
B. Orchid
C. Cuscuta D. Tinospora
Solution: The parasitic plant produces some knob like roots at the point of attachment with the host plant known as haustoria which penetrate into the host plant and draws nourishment. Therefore, the correct answer is option c.
Stem
You possibly know about a stem since you were a kid. Then what are we going to do now? We will know more about a stem! Stems play an important role in any plant. No, it is not just transportation of water and minerals! There is more to the story indeed! Let us look at the details of plant stems in this chapter. We will look at their
characteristics and types as well. This is an important concept and will help you score better in your exams!
What is a Stem?
The stem is the ascending part of the axis bearing branches, leaves, flowers and fruits. It develops from the plumule of the embryo of a germinating seed. It bears nodes and internodes. What are nodes and
internodes? The regions of the stem where leaves are born are called nodes. On the other hand, internodes are the portions between two nodes.
The stem bears buds, which may be terminal or axillary. Now, let us look at what the functions of a stem are.
Functions of the Stem
The stem performs the two major functions of
● Spreading out branches bearing leaves, flowers and fruits.
● Conducting water, minerals and photosynthates.
Learn more about the Morphology of Leaf and Fruits here.
However, many a time stems also have various modifications. These help the stem to perform the function of storage of food, support, protection and vegetative propagation. Before we proceed to know more about such modifications, let us look at the various
characteristics of stems.
Characteristics of Stems
● The stem is an ascending axis of the plant and develops from the plumule and epicotyl of the embryo.
● It is generally erect and grows away from the soil towards the light. Therefore, it is negatively geotropic and positively phototropic.
● The growing apex of stem bears a terminal bud for growth in length.
● In flowering plants, the stem is differentiated into nodes and internodes.
● The lateral organs of the stem (i.e., leaves and branches) are exogenous in origin (i.e., from the cortical region).
● The young stem is green and photosynthetic.
● Hair, if present, are generally multicellular.
● In mature plants, stem and its branches bear flowers and fruits.
Now that we know quite a few things about stems, let us look at the various modifications of stems. This is an important aspect of this chapter. Hence, you must pay extra attention to it.
Modifications of Stem
Too often, stems are modified to perform a range of functions. Below, we will discuss in brief about the various modifications of stems.
● Modification of Stems for the Storage of Food: Underground stems of potato, ginger, turmeric, zaminkand, colocasia are modified to store food in them. They also act as organs of perennation to tide over conditions unfavourable for growth.
● Modifications for support: Stem tendrils which develop from axillary buds, are slender and spirally coiled and help plants to climb such as in gourds (cucumber, pumpkins, watermelon) and grapevines.
● Stem modifications for defence: Axillary buds of stems may also get modified into woody, straight and pointed thorns.
Thorns are found in many plants such as Citrus, Bougainvillea.
They protect plants from browsing animals.
● Modification of stems for photosynthesis: Some plants of arid regions modify their stems into flattened (Opuntia), or fleshy cylindrical (Euphorbia) structures. They contain chlorophyll and carry out photosynthesis. Besides these, stems can also be modified for vegetative propagation.
Thus, we see the characteristics and functions of the stem. We also went through the concept of various modifications of stems. A
modification is important in various organs of the plants as they help to perform separate functions. At times, these functions are crucial for the existence of the plants.
Solved Examples for You
Q1: Explain the modification in stems for vegetative propagation.
Ans: At times, the stems of the plants can be modified to serve various purposes. They include:
● Runner: Underground stems of some plants spread to new niches and when older parts die new plants are formed. e.g., grass and strawberry
● Stolon: In these plants, a slender lateral branch arises from the base of the main axis and after growing aerially for some time arch downwards to touch the ground. e.g., mint and jasmine
● Offset: A lateral branch with short internodes and each node bearing a rosette of leaves and a tuft of roots are found in aquatic plants. e.g., Pistia and Eichhornia.
● Sucker: In these, the lateral branches originate from the basal and underground portion of the main stem, grow horizontally beneath the soil and then come out obliquely upward giving rise to leafy shoots. e.g., banana, pineapple and
Chrysanthemum.
Q2: Ginger is a stem which can be differentiated from root because it:
a. Grows parallel to the ground b. Stores food
c. Lacks chlorophyll
d. Has nodes and internodes
Ans: A rhizome is a thick horizontally growing stem. It has nodes and internodes as well as scale leaves, axillary buds, adventitious roots and a terminal bud. Hence the answer is d.
The Fruit
Almost all of us love all types of fruits! However, have you ever thought about how complex the fruits can be? Yes! Fruits are of various types, with different characteristics and each one with a distinct scientific name! So, what’s your favorite fruit? Mango? But, how much do you know about it, apart from the fact that it is tasty! In this topic, we will read more about the various types and characteristics of fruits.
The Fruit
Fruits protect the seeds. Yes! This is the primary function of the fruits and not just satisfying your taste buds! But, in some fruits, seeds are absent. Examples include grapes, banana, etc. They are parthenocarpic or seedless fruits. Let us now look at the various parts of the fruit in greater detail.
Browse more Topics under Morphology Of Flowering Plants
● Flower
● Inflorescence
● Leaf
● Root
● Stem
● The Seed
● Classification of Flowering Plant
Pericarp
After ripening, the ovarian wall changes into pericarp. This pericarp may be thick and fleshy or thick and hard or thin and soft. The pericarp has 3 layers. They are
● Outermost layer: Epicarp
● Middle layer: Mesocarp
● Innermost layer: Endocarp
Now we move on to know more about the various types of fruits.
True Fruit
A true fruit is one that develops only from the ovary. Examples are Mango, Coconut, Zizyphus, etc.
False Fruit or Pseudocarp
In some fruits, it is not the ovary that forms the fruit. In fact, some other parts of the flower, like the thalamus, inflorescence, calyx are modified to become a part of the fruit. These types of fruit are called false fruits. Examples are Apple, Strawberry, etc.
Know more about Flower
Classification of Fruits
There are two criteria for the classification of fruits:
● Whether the carpels present in gynoecium are free or in a fused state.
● One or more flower takes part in the formation of fruit.
According to the above points, we can classify fruits into types of fruits
Types of Fruits
● Simple
● Aggregate
● Composite
Simple fruit
These fruits develop from the monocarpellary ovary or multicarpellary syncarpous ovary. Only one fruit is formed by the gynoecium. Simple fruits are of two types
● Fleshy Fruits: In fleshy fruits, the fruit wall is differentiated into epicarp, mesocarp, and endocarp. These fruits develop from superior or inferior syncarpous gynoecium.
● Dry Fruits: The pericarp of simple dry fruits is usually quite dry and hard. It is not differentiated into the three layers of epicarp, mesocarp and endocarp. In some dry fruits, this pericarp is broken down and the seeds are scattered or dispersed. These fruits are dehiscent fruits.
In some fruits, the pericarp is further arranged into one or more seeded segments. Such fruits are schizocarpic fruits. In some fruits, the pericarp is not observed to be dehisced even after maturing/ripening.
Such fruits are indehiscent Fruits.
What is Inflorescence?
Aggregate Fruits
These are the fruits that develop from the multicarpellary apocarpous ovary. It becomes a fruitlet because each carpel is separated from one another in the apocarpous ovary. These fruits make a bunch of fruitlets which is known as etaerio.
● Etaerio of follicles: Each fruit or etaerio is a follicle. Eg.
Calotropis, Catharanthus, Magnolia -e. In calotropis, the stigma
is fused or joined in carpellary ovary and ovaries of ovules are separated. It means only two follicles are present in etaerio.
● Etaerio of achenes: In this aggregate fruit, each fruit is an
achene. Eg. Ranunculus, Strawberry, Rose, Lotus. In lotus, the thalamus becomes spongy and some achenes are embedded in it. In strawberry, the thalamus is fleshy and we can find small achenes on its surface.
● Etaerio of berries: It is an aggregate of small berries. Eg.
Polyalthia, Annona squamosa (Custard-apple). In the etaerio of Annona, all the berries are arranged densely on the thalamus.
● Etaerio of drupes: In this type of fruit, many small drupes develop from different carpels. Eg. Raspberry. In this type carpel of apocarpous ovary form drupe fruit.
Composite Fruits
All composite fruits are false fruits. In these fruits, generally, there are many ovaries and other floral parts combining to form the fruit. These are of two types:
● Sorosis: These fruits develop from spike, spadix or catkin inflorescence. Examples inJackfruit fruit, Kevda (screwpine).
In jackfruit (Kathal) pistillate flowers are developed around the peduncle. In fruit formation, the pericarp becomes spongy and fused.
● Sycosis: These fruits develop from hypanthodium
inflorescence. Receptacle becomes hollow and has a pore.
Numerous small scales surround the pore. Eg. Ficus species Peepal
Understand Classification of Flowering Plant
Geocarpic Fruit
These are underground fruits. Examples include Arachis.
Solved Examples for You
Question: Write a note on the dispersal of fruits and seeds.
Solution: Most of the plants do not move from one place to another.
They grow, produce flowers and fruits while remaining fixed at one and the same place. The seeds falling directly under the mother plant have to germinate and develop under limited food supply and space.
To overcome this problem, the fruits and seeds have several special devices for wide dispersal. The natural agents like wind, water and animals and even the mechanism of dehiscence in some fruits, help
the seeds and fruits to disperse from one place to another, and to long distances from the parent plant.
● Wind: In the species where the seeds are light in weight or have some accessory part to help dissemination, are dispersed by the air current.
● Water: The fruits and seeds with specialized devices which may be in the form of spongy and fibrous outer walls as in coconut and spongy thalamus as in lotus, and small seeds with airy aril as in water lily, float very easily in water and are carried away to long distances with the water current.
● Animals: The fruits and seeds with hooks, spines, bristles, stiff hair, etc., get attached to the body of hairy and woolly animals and are carried away by them to distant places. For instance fruits of Xanthium and Urena bear curved hooks, spear grass has a bunch of stiff hair, Tribulus has sharp and rigid spines.
The Seed
You, of course, hate the seed when you are savouring your favourite watermelon. However, are you aware that without the seeds, you can’t
get to eat and enjoy that fruit at all? Seeds are important for plants in more ways than you can actually imagine! In this chapter, we will look at the types of seed and study about their characteristics in more detail.
What is the Seed?
A seed is a basic part of any plant. The ovules after fertilization, develop into seeds. A seed is made up of a seed coat and an embryo.
The embryo is made up of a radicle, an embryonal axis and one (wheat, maize) or two cotyledons (gram and pea). A seed is found inside a fruit which converts into a new plant when we plant it. Hence, the seed is the most important part.
Let us now look at the different types of seeds and study their characteristics.
Types of Seeds
A Seed is primarily of two types. The two types are:
● Monocotyledonous Seed
● Dicotyledonous Seed
Let us now study about these types of seeds in brief.
Structure of a Monocotyledonous Seed
A Monocotyledonous seed, as the name suggests, has only one cotyledon. There is only one outer layering of the seed coat. A seed has the following parts:
● Seed Coat: In the seed of cereals such as maize, the seed coat is membranous and generally fused with the fruit wall, called Hull.
● Endosperm: The endosperm is bulky and stores food.
Generally, monocotyledonous seeds are endospermic but some as in orchids are non-endospermic.
● Aleuron layer: The outer covering of endosperm separates the embryo by a proteinous layer called aleurone layer.
● Embryo: The embryo is small and situated in a groove at one end of the endosperm.
● Scutellum: This is one large and shield-shaped cotyledon.
● Embryonal axis: Plumule and radicle are the two ends.
● Coleoptile and coleorhiza: The plumule and radicle are enclosed in sheaths. They are coleoptile and coleorhiza.
Learn more about the Morphology of Flower here.
Structure of a Dicotyledonous Seed
Unlike monocotyledonous seed, a dicotyledonous seed, as the name suggests, has two cotyledons. It has the following parts:
● Seed coat: This is the outermost covering of a seed. The seed coat has two layers, the outer testa and the inner tegmen.
● Hilum: The hilum is a scar on the seed coat through which the developing seed was attached to the fruit.
● Micropyle: It is a small pore present above the hilum.
● Embryo: It consists of an embryonal axis and two cotyledons.
● Cotyledons: These are often fleshy and full of reserve food materials.
● Radicle and plumule: They are present at the two ends of the embryonal axis.
● Endosperm: In some seeds such as castor, the endosperm formed as a result of double fertilisation, is a food storing tissue. In plants such as bean, gram and pea, the endosperm is not present in the matured seed. They are known as
non-endospermous.
Solved Question for You
Question: What are the types of mature seeds?
Solution: We know two types of mature seeds. These are:
● Non-albuminous – These seeds do not contain any residual endosperm to store the food. Example: pea, groundnut.
● Albuminous – These seeds consist of an endosperm to function as a storage for the food. Example: wheat, maize.
Classification of Flowering Plant
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.
1) Dicotyledons
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.
2) Monocotyledons
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).
