- 1 Parts and Types of Flower – Flower as a modified Shoot
- 1.1 Morphology of Flower
- 1.2 Parts of a Typical Flower (China Rose) and Their Functions
- 1.3 Types of Flower
- 1.4 Regular Flower and Irregular Flower
- 1.5 Symmetry of Flowers
- 1.6 Complete and Incomplete Flower
- 1.7 Spiral, Cyclic, and Hemicydic Flowers
- 1.8 Isomerous, Trimerous, Tetramerous, and Pentamerous Flowers
- 1.9 Monoecious, Dioecious, and Polygamous Plant
- 1.10 Flower as a modified Shoot
The study of marine Biology Topics reveals the incredible diversity and complexity of life in the oceans.
Parts and Types of Flower – Flower as a modified Shoot
Sexual reproduction is the important process of the development of new organisms through the formation and fusion of two different gametes. Sexual reproduction involves two processes which rearrange the genes and reduce the number of chromosomes and fertilization, which restores the chromosome to a complete diploid number. The evolutionary origin and adaptive significance of sexual reproduction relate to the evolution of sexual reproduction. In the case of flowering plants, the gametophytes are relatively small and the sporophyte is much larger. All flowering plants perform sexual reproduction. In flowering plants, gametes are formed inside specialized reproductive organs called flowers.
The amazing diversity among the floral parts of the plant shows a great range of adaptations to ensure the formation of the end products of sexual reproduction, i.e., fruits and seeds. According to biologists, flowers are the finest morphological as well as embryological marvels and the sites of sexual reproduction.
In flowering plants, the flower bud is formed as a specially metamorphosed shoot. This flower bud gradually develops into a mature flower. Flower is the most beautiful and attractive organ of the plant body. It is variously colored and possesses a pleasant odour. A flower, sometimes known as a bloom or blossom and is called the reproductive organ of a plant as it takes part in reproduction and plays an important role in the formation of new plants. Flowers, fruits, and seeds are developed. Seeds germinate to form new plants.
The biological function of a flower is to affect reproduction, usually by providing a mechanism for the union of sperm with eggs. Flowers may facilitate outcrossing (fusion of sperm nuclei and eggs from different individuals in a population) or allow selling (fusion of sperm nuclei and eggs from the same flower). Some flowers produce diaspores without fertilization (parthenocarpy). Flowers contain sporangia and are the site where gametophytes develop. Flowers give rise to fruits and seeds. Many flowers have evolved to be attractive to animals, so as to make them vectors for the transfer of pollen.
Characteristics of Flower
- The flower is a modified shoot.
- Flower is a temporary plant organ, i.e., develops for a certain period of time.
- It develops from the shoot apex or axils of the leaf or bract.
- It is of various forms, colours and possesses a pleasant odour.
- It takes part in the reproduction of plants.
- It bears floral leaves.
- Fruits and seeds develop from the flower.
The flower is a modified and condensed shoot meant for reproduction.
Morphology of Flower
A complete flower has the following parts: Calyx, Corolla, Androecium, and Gynoecium. A typical flower has also other two parts like the pedicel and thalamus. The parts of a typical flower are shown in the following table-
In addition to facilitating the reproduction of flowering plants, flowers have long been admired and used by humans to beautify their environment, and also as objects for romance, ritual, religion, medicine, and as a source of food.
Parts of a Typical Flower (China Rose) and Their Functions
A flower in which all the floral parts i.e., pedicel, thalamus, calyx, corolla, androecium, and gynoecium with their normal functions are present, is called a typical flower, e.g., China rose.
A stereotypical flower consists of four kinds of structures attached to the tip of a short stalk. Each of these parts is arranged in a whorl on the receptacle. The four main whorls (starting from the base of the flower or lowest node and working upwards) are as follows:
Each individual flower is borne at the tip of a specialized stalk, called the pedicel.
Function: It connects the flower with the stem or branch or sub-branches.
The apex of the pedicel which supports the floral parts, is termed as thalamus. The floral leaves are arranged on the thalamus in a regular order either spirally or in a cyclic manner.
Function: Thalamus bears the floral whorls, i.e., calyx, corolla, androecium, and gynoecium.
C. Floral Whorls
1. Calyx: It is the outermost and lowermost whorl of floral members and is composed of green leaf-like structures, the sepals. In China rose the sepals are five in number, green, and fused together in their basal part forming a bell-shaped structure. Calyx with fused sepals is called the gamosepalous calyx.
In China rose below the calyx there is another whorl of green parts consisting of about five or six members, called the epicalyx. The individual members remain free.
- Calyx protects the inner parts of the bud from excessive heat, cold, rain, and other adverse conditions.
- Sepals being green perform the general function of leaves.
- Where the sepals are coloured they attract insects and help in pollination.
2. Corolla: The second whorl from outside towards the center is the Corolla. The individual members of the corolla, are called petals. The petals are usually brightly coloured. In China rose, there are five red coloured petals. Petals are free and are arranged in twisted aestivation. Each petal is narrower at the base and broader at the above. The bases are fused with the staminal column of the flower.
- Corolla protects the inner essential whorls from external injury.
- Corolla is brightly colored structures and attracts insects for pollination.
3. Androeciltm: It is the third inner whorl and is composed of some slender, elongated structures, called stamens. Each stamen consists of a basal elongated portion, the filament, and a terminal enlarged pollen-producing portion, the anther. In china rose, there are numerous stamens, whose basal filamentous parts are fused together to form a staminal column. The upper smaller parts of the filaments and the anthers are free. The anthers are kidney-shaped and contain many yellow-colored, spiny pollen grains.
- Stamens produce pollen grains.
- Pollens produce male gametes and help in fertilization.
4. Gynoecium: It is the innermost central whorl and is composed of female parts called carpels. Gynoecium may contain a single carpel or two too many carpels. In the case of many carpels, they may remain free or united together. In china rose, there are five carpels fused together forming a compound pistil. The compound pistil consists of a syncarpous ovary, a long, slender, thread-like style, and five stigmas. The ovary is superior, 5-chambered with axile placentation. A sterile and undeveloped pistil is called a pistillode.
- It produces the embryo sac in which, after fertilization, the embryo develops.
- Ovary after fertilization matures to form the fruit which contains seeds.
Types of Flower
Many flowers have symmetry. When the perianth is bisected through the central axis from any point, symmetrical halves are produced, forming a radial symmetry. These flowers are also known to be actinomorphic or regular, e.g., rose or Trillium. When flowers are bisected only by one line that produces symmetrical halves the flower is said to be irregular or zygomorphic, e.g., Snapdragon or most orchids.
Regular Flower and Irregular Flower
On the basis of form and structure of different whorls of a flower, they are of two types:
- Regular flower: When the floral parts of each whorl of a flower are similar in size and shape, the flower is called a regular flower, e.g., China rose (Hibiscus rosa-sinensis), Datura (Datura metal), etc.
- Irregular flower: When any of the floral parts of any whorl of a flower is dissimilar in size and shape, the flower is called an irregular flower, e.g., Pea (Pisum sativum), Clitoria ternatea, etc.
Symmetry of Flowers
The arrangement of the floral members around the thalamus of a flower is known as floral symmetry. On the basis of the floral symmetry, flowers may be of the following three types:
- Actinomorphic: A flower that can be divided into two equal and symmetrical halves by any vertical plane passing through the axis, is called an actinomorphic flower, e.g., Hibiscus, Solarium, etc.
- Zygomorphic: A flower that can be divided into two equal and symmetrical halves by one particular plane only passing through the axis, is called a zygomorphic flower, e.g., Pisum, Clitoria, etc.
- Asymmetric: A flower that cannot be divided into two equal halves by any vertical plane passing through the axis, is called an asymmetric flower, e.g., Canna, Vanda, etc.
The four main parts of a flower are generally defined by their positions on the receptacle and not by their function. Many flowers lack some parts or parts may be modified to perform other functions and/or look like what is typically another part. In some families, like Ranunculaceae, the petals are greatly reduced and in many species, the sepals are colorful and petal-like, the double flowers of Peonies and Roses are mostly petaloid stamens. Flowers show a great variation and plant scientists describe this variation in a systematic way to identify and distinguish species.
Complete and Incomplete Flower
- Complete Flower: A flower is said to be complete when all four floral whorls are present as in China rose (Hibiscus rosa Sinensis), Pea (Pisum sativum), Datura (Datura metel), etc. Complete flowers are always bisexual.
- Incomplete flower: A flower is said to be incomplete when any one or more of the four floral whorls are absent as in Beta sp., Cucurbita sp., gourd, etc.
In an incomplete flower when one of the accessory whorls (calyx or corolla) is absent (i.e., perianth present), the flower is called monochlamydeous as in tuberose. In flowers when both calyx and corolla are present, it is called dichlamydeous, e.g., Pea. An incomplete flower with only androecium (gynoecium absent) is called a male or staminate flower, whereas an incomplete flower with the only gynoecium (androecium absent) is called a female or pistillate flower, e.g., Gourd. When both androecium and gynoecium are absent or non-functional in a flower, the flower is called a neuter flower, e.g., Arum, ray floret of sunflower. When either androecium or gynoecium or both are present in a flower but without calyx and corolla, then the flower is called nude or naked or achlamydeous flower, e.g., Euphorbia, Arum, etc.
Spiral, Cyclic, and Hemicydic Flowers
The floral members are borne on the thalamus in three ways. Accordingly, the flower may be of the following types:
1. Spiral: When the floral members are borne spirally on an elongated thalamus, the flower is called a spiral flower, e.g., Paeonia, or Eupomatia. The spiral arrangement of floral members is a primitive character.
2. Cyclic: When the floral members of each whorl are borne in a cyclic manner on the comparatively shorter thalamus, the flower is called a cyclic flower, e.g., Hibiscus, Datura. The cyclic arrangement of floral whorls is an advanced characteristic.
3. Spirocyclic or Hemicydic: When the floral members are borne partly in a spiral manner and partly in a cyclic manner on the thalamus, the flower is called a spirocyclic flower, e.g., Magnolia, Nymphaea.
Isomerous, Trimerous, Tetramerous, and Pentamerous Flowers
1. Isomerous flower: When the number of floral members in each whorl of a flower remains the same or an exact multiple of the same, then the flower is called an isomerous flower, e.g., china rose.
2. Trimerous flower: When the number of floral members in each whorl of a flower is three or multiples of three, the flower is called a trimerous flower, e.g., Grasses. Trimerous flowers are common in monocotyledonous plants.
3. Tetramerous flower: When the number of floral members in each whorl of a flower is four or multiples of four, the flower is called a tetramerous flower, e.g., Ixora, Oldenlandia.
4. Pentamerous flower: When the number of floral members in different whorls of the flower is five or multiples of five, the flower is called a pentamerous flower, e.g., China rose, Datura, etc., pentamerous flowers are common in dicotyledonous plants.
In some flowers, the calyx and corolla can not be distinguished. There is only one set of accessory members that can neither be termed calyx, nor corolla, the accessory whorl is called perianth, e.g., Tuberose (Polianthes sp.).
Monoecious, Dioecious, and Polygamous Plant
1. Monoecious Plant: When a plant bears both kinds of unisexual flowers (staminate and pistillate flower) or only bisexual flowers, the plant is called a monoecious plant, e.g., Gourd, China rose.
2. Dioecious Plant: When a plant bears only one kind of flower either staminate or pistillate, the plant is called a dioecious plant, e.g., Palmyra palm, Carica papaya, etc.
3. Polygamous Plant: When a plant bears more than one type of flower – staminate flower, pistillate flower and neuter flower, or bisexual flower, the plant is called a polygamous plant, e.g., Mango, Litchi, etc.
Differences between Flower and Inflorescence:
|1. It is a modified shoot.||1. It is a group of flowers arranged on a floral axis.|
|2. It shows distinct nodes and internodes.||2. It does not show distinct nodes and internodes.|
|3. The stalk of the flower is called a pedicel.||3. The stalk of the inflorescence is called a peduncle.|
Differences between Complete and Incomplete Flower:
|Complete Flower||Incomplete Flower|
|1. All four floral whorls calyx, corolla, androecium, and gynoecium are present.||1. It lacks one or more of the four floral whorls.|
|2. It is always bisexual.||2. It may be bisexual or unisexual or neutered (sterile).|
|3. In this case, both the accessory floral whorls are always present.||3. In this case, two or one (Perianth) accessory floral whorls are present or may not be present (Nude flower).|
|4. It is regarded as a typical flower. Examples: Hibiscus, Datura.||4. It is not regarded as a typical flower. Examples: Cucurbita, Polianthes.|
Differences between Regular and Irregular Flower:
|Regular Flower||Irregular Flower|
|1. In this flower, the floral members of each whorl are equal in size and shape.||1. In this flower, floral members of one or more of the whorls are unequal in size and shape.|
|2. This type of flower is always actinomorphic. Examples: Hibiscus, Datura, etc.||2. This type of flower is either zygomorphic or asymmetric. Examples: Clitoria, Pisum, etc.|
Flower as a modified Shoot
Although a flower is not similar in external appearance to a vegetative shoot on the basis of origin, position, and structure of both, the flower is considered as a modified shoot. The flower is a modified shoot which may be confirmed from the following points:
1. Axis Nature of the Thalamus
(a) The axis nature of the thalamus is not very clear as the internodes are so much condensed. But in certain exceptional cases, the internodes are elongated showing the stem character. Such type of internodes are seen in Cleome gynandra, Capparis sepiaria, Passiflora suberosa etc. In Passiflora suberosa, the elongated internode between the corolla and androecium is called an androphore. Similarly, the elongated internode between androecium and gynoecium is called gynophore which is found in Cleome gynandra, Capparis septaria, etc.
(b) The growth of the thalamus is limited by the carpels but sometimes the thalamus grows beyond the gynoecium and bears a leafy shoot or a flower above the first flower. Such monstrous development has been seen in Rose, pear, and some other cases.
(c) In Michelia champaca, Polyalthia longifolia, etc., the region of the thalamus bearing carpels elongates like an ordinary stem giving rise to an aggregate fruit.
(d) The internal structure of the shoot and the thalamus is similar and the vascular supply to floral leaves resembles the vascular supply of leaves.
2. Nature of Floral Leaves
The sepals, petals, stamens, and carpels exhibit their leaf nature in the following:
- The floral leaves are borne on the thalamus in the same pattern as the leaves on the stem. They may arise in whorls or spiral fashion.
- The four types of floral members (i.e., sepals, petals, stamens, and carpels) and foliage leaves often change from one to the other.
- The floral members of Nymphaea (water lily) show all stages between a sepal and petals and between petals and a stamen by the gradual transition.
- In Peony (Paeonia) one can see the transition from leaves to sepals and from sepals to petals showing the identical nature of all of them.
- In the green rose the sepals look like foliage leaves and even the petals are green and leafy.
- In Mussaenda frondosa one of the sepals looks out of proportion in the calyx as it is large and with distinct veins like a leaf but pigmented like a petal.
- Carina flowers show petaloid stamens.
- In flowers of leguminous plants like peas, beans, etc. the carpel clearly looks like a folded green leaf.
- In certain primitive flowers such as Degeneria. Stamens are expanded like leaves.
- Carpels also become petaloid or sepaloid in Zinnia etc.
3. Similarities between Floral Buds and Vegetative Buds
- A flower arises from a bud like the vegetative bud.
- Both floral buds and vegetative buds arise either from the axils of leaves or from the apex of the shoot.
- In plants like Agave americana, the transformation of floral buds into vegetative buds is shown.
- In Globba bulbifera transformation of floral buds into bulbils is observed.
- In Ananas comosus buds present at the apex of the inflorescence axis, take part in propagation.
From the above discussion, it may be concluded that the flower is actually a modified shoot.