Flower : Flower is an important shoot meant for sexual reproduction. In a flower there are sepals, petals, stamens and carpels the four types of floral leaves. Sepals and petals are floral leaves. These are non-essential organs. Stemens and carpels are ‘essential’ organs.
Parts of a Flower
A typical flower consists of four parts. These are (a) Calyx, (b) Corolla,
(c) Androecium and (d) Gynoecium.
Complete Flower : A flower which has all 4 types of floral leaves is called a complete flower.
Incomplete flower : A flower in which any one type of floral leaves is absent is called incomplete flower.
Conditions
(a) Monoecious : Monoecious plant has both male and female flowers, e.g. Cocos, nucifera.
(b) Dioecious : Dioecious plant has male and female flowers on different plants, e.g. Borassus.
(c) Polygamous : In polygamy the same plant has unisexual and bisexual flowers, e.g. Mangifera.
Symmetry of Flowers
(a) Acyclic symmetry : This is also called spiral symmetry. In it, the floral parts are arranged spirally on conical thalamus, e.g. Maganolla.
(b) Hemicyclic : In it symmetry perianth lobes are arranged in circles. Stamens and carpels are arranged spirally, e.g. Annona.
(c) Cyclic : In this symmetry floral parts are arranged in circles on thalamus, e.g. Datura.
Merosity
Merosity is of two types namely—(a) Isomerous and (b) Anisomerous.
In isomerous similar number of floral parts or in multiples of that number are present. They are—
(i) Dimerous, (ii) Trimerous, (iii) Tetramerous, (iv) Pentamerous and (v) Polymerous.
In anisomerous the floral parts in different whorls are in different numbers, e.g. Achras sapota.
Structural Symmetry
Structural Symmetry of flowers are of three types; namely,
(a) Actinomorphic flower
(b) Zygomorphic flower
(c) Assymmetric flower.
(a) Actinomorphic flower : This is also called regular symmetry. Flower in this symmetry can be divided into two equal halves, longitudinally, e.g. Hibiscus.
(b) Zygomorphic flower : This is also called monosymmetrical. In this symmetry, flower can be divided into two equal and similar halves in vertical only, direction, e.g. Ocimum.
(c) Assymmetrical flower : This is also called irregular symmetry. In this symmetry, flower can not be divided into two equal and similar halves in any vertical direction, e.g. Canna indica.
Position of Gynoecium on the Thalamus
There are three positions of Gynoecium on the thalamus—
(a) Hypogynous (b) Perigynous and (c) Epigynous.
(a) Hypogynous : The gynoecium is located at the apex of the convex Thalamus. Calyx, corolla and androecium are arranged at the base of the gynoecium. Such a flower is called hypogynous. The ovary is said to be superior, e.g. Annona, solanum.
(b) Perigynous : Thalamus is concave or saucer shaped. The floral parts like calyx, corolla, and androecium are brought to the same level. Such a flower is called perigynous. This type of ovary is half superior or half inferior, e.g. Crotalaria, Cassia.
(c) Epigynous : Thalamus has a deep cup like structure. It fuses with the ovary completely. Floral parts are present above the ovary arising on the rim of the Thalamus. Such a flower is called Epigynous. The ovary is said to be inferior, e.g. Helianthus.
Bract
Bracts are condensed leaf like structures on the peduncle. All flowers come only in the axils of bracts. Bracts protect the flower in the bud condition. Bracts are of the follwoing types—
(a) Foliaceous bract : Bracts are coloured; ordinarily green foliage leaf, e.g. Adathoda.
(b) Petaloid bract : Bracts are petal like brightly coloured. They perform the function of petals.
(c) Involucre : It is a whorl of bracts of flowers, present in the circumfrence of an inflorescence, fused to give protection.
(d) Scaly bracts : Bracts are reduced to scale like structures, e.g. Helianthus.
(e) Glume : Glumes are two scaly bracts present at the base of spikelet in poaceae.
(f) Spathe : Spathe is a large, thick boat shaped bract covering the whole inflorescence, e.g. Musa.
(g) Epicalyx : These small bracts are arranged in a circle below the Calyx, e.g. Hibiscus.
Thalamus : It is also called Receptacle or Torus. Thalamus is a condensed axis of the flower. It has four nodes. Internodes are clearly seen in some flowers.
1. Anthophore : The elongated internode is present between calyx and corolla of a flower and it is developed into a stalk like structure, e.g. Silence.
2. Androphore : The elongated internode between corolla and androecieum developed into a stalk like structure, e.g. Gynandropsis.
3. Gynophore : It is found that in some flowers the internode between androecium and gynoecium develops into a stalk like structure, e.g. Capparis.
4. Gynandrophore : The internode on the axis of flower is like stalk and bears both androecium and gynoecium at its apex, e.g. Passiflora.
5. Carpophore : In it thalamus grows into the gynoecium and connects the carples, e.g. Coriandrum.
6. Disc : The floral axis is present below the gynoecium like a small disc, e.g. Citrus species.
Perianth : Perianth is constituted by the calyx and corolla together. It is a non-essential organ of the flower. It protects the inner essential organs like androecium and gynoecium. Calyx is green in colour and corolla is multicoloured.
1. Achlamydeous flowers : Perianth is not there and the flowers are naked, e.g. Male and female flowers of cyanthium inflorescence.
2. Chlamydeous flowers : Flowers are with perianth.
(a) Monochlamydeous : Perianth is arranged in one whorl, e.g. Croton and Amaranthus.
(b) Dichlamydeous : Perianth is arranged in two whorls.
(i) Homochlamydeous : The two whorls of a flower are similar without any differentiation, e.g. Allium.
(ii) Heterochlamydeous : Perianth is arranged in two whorls and they can be differentiated into calyx and corolla, e.g. Datura and Hibiscus.
Aestivation
Aestivation is the mode of arrangement of perianth lobes during bud condition.
1. Open : Perianth lobes are free and remain open with wide gaps between them, e.g. Calyx of Brassica.
2. Valvate : The perianth lobes are arranged closely with small gaps between them. They remain free or united, e.g. Calyx of Annona and Corolla of Brassica.
3. Twisted : The lobes overlap with each other, e.g. Corolla of Datura.
4. Imbricate : It is a type of twisted aestivation found in corolla. The overlapping of the petals is in 1 + 1 + 3 manner.
5. Quincuncial : It is also a type of twisted aestivation. In this the perianth lobes overlap in 2 + 2 + 1 manner.
8. Flower
Calyx is a group of sepals. These sepals of a calyx are the essential organs of a flower which are thin, expanded and green coloured. They provide protection to the flower during bud condition.
Calyx Modification
1. Petaloid : Sepals are coloured and look like petals, e.g. Tamarindus.
2. Pappus : Sepals have hair like structures and are called ‘pappus’, e.g. Sunflower family.
3. Spinous : Sepals are modified into two persistant spines on either side of the fruit, e.g. Trapa.
4. Hooded : One of the sepals covers the flower, and expanded e.g. Aconitum.
5. Spurred : One sepal in the flower is elongated into a tube and grows downwards, e.g. Impatients.
6. Succulent : These sepals store water along with gelatinous substance, e.g. Dellinia.
Corolla
Corolla is a non-essential part of a flower. The corolla lobes are coloured and attractive, and are called ‘petals’. They carryout cross pollination by attracting insects.
Shapes of Polypetalous Corollas
1. Sepaloid : Petals appear dark green or light green, e.g. Annona and Artabotry.
2. Saccate : Petals are tubular with an apical sac-like structure.
3. Spurred : Two petals grow tubular with a pointed base, e.g. Delphinum.
4. Coronary : In coronary at the tip of the petals, a crown like structure is formed, e.g. Passiflora.
5. Cruciform : In cruciform cross shaped corolla contain four petals of which each petal is clawed, e.g. Brassica.
6. Rosaceous : The corolla contains five symmetrical petals. Each petal is narrow at the base and broad, triangular at the apex, e.g. flowers of Malvaceae and Rosaceae.
7. Caryophyllaceous : There are five symmetrical clawed petals and each petal has a narrow stalk-like base, with an apex arranged at right angle to the base, e.g. Dianthus.
8. Papillionaceous : In this the corolla has 5 unequal petals of which the largest petal is arranged opposite to the axis. On either side of this, two winged petals are present. Remaining two petals appear like the base of a boat, e.g. Dolichos.
Types of Gamopetalous and symmetrical corollas :
1. Tubular.
2. Companulate.
3. Infundibuliform or Funnel shaped.
4. Rotate.
5. Hypocrateriform or Salver shaped.
Types of Gamopetalous and asymmetrical corollas :
1. Bilabiate
2. Ligulate
3. Personate.
Androecium
Androecium is an organ containing stamens. These are male reproductive organs and produce pollen grains. The sterile stamens are called ‘staminodes’.
Parts of a stamen : Stamen has three parts—1. Filament, 2. Anthers and 3. Connective.
Attachment of filament to anther lobes
1. Basifixed : In it, the tip of the filament is fused with the base of anther lobe, e.g. Datura.
2. Dorsifixed : The filament is attached to the anther on the mid dorsal side, e.g. Annona and Passiflora.
3. Adnate : The filament extends from the base to the apex of the anther lobes, e.g. Nelumbo.
4. Versatile : The apex of the filament is pointed and is attached to the back of the anther as a point so that the anther lobes swing freely on any direction, e.g. Oryza sativa.
1. Didynamous : There are four stamens in androecium in which two are long and two are short, e.g. Ocimum.
2. Tetradynamous : There are six stamens in androecium arranged in two whorls. The outer two stamens are shorter and the inner four are longer, e.g. Brassica.
3. Inserted stamens : It has been seen that in some flowers the filaments are shorter than the petals, e.g. Datura and Dolichos.
4. Exerted stamens : In some flowers the filaments of the stamens are longer than the petals, e.g. Acacia arabica.
Arrangement of stamens
1. Haplostemonous : In a flower all the stamens are arranged in one whorl, e.g. Solanum.
2. Diplostemonous : In a flower all the stamens are arranged in two whorls, e.g. Cassia sps.
3. Obdiplostemonous : Stamens are arranged in two whorls and outer whorl is opposite to corolla lobes, e.g. Murraya exotica.
Cohesion of stamens : Cohesion of stamens includes the fusion among filaments, or anther lobes or both. The number is,
(i) Monadelphous : The filaments of all the stamens form one bundle, e.g. Hibiscus.
(ii) Diadelphous : In a flower, out of ten stamens nine stamens are fused to form one bundle and the 10th remains free as a second bundle, e.g. Dolichos.
(iii) Polyadelphous : The stamens are fused to form many bundles, e.g. Cieba pentandra.
Syngenesious : The anther lobes are united, leaving their filaments free.
Synandry : The complete fusion of anthers takes place e.g. Cucurbita.
Adhesion : Adhesion is defined as the fusion of stamens with other parts of the flower arranged in different whorls like calyx, corolla and gynoecium. Adhesion is of four types.
(i) Episepalous : Stamens are attached to the sepals of outer whorls.
(ii) Epipetalous : Stamens adhere to the corolla lobes.
(iii) Epiphyllous or Epitepalous : Stamens adhere to the inner margins of perianth lobes.
(iv) Gynostegium : Stemens are attached to the stigmas of gynoecium.
Dehiscence of Anthers : It is of four types.
1. Longitudinal.
2. Transverse.
3. Valvular.
4. Porous.
Gynoecium
It is the female reproductive organ. It is also considered as the inner whorl of the essential organs, formed from carpels. They participate in sexual reproduction and produce fruits and seeds.
Strucutre of Gynoecium : Gynoecium has three parts.
(a) Basal swollen part (ovary).
(b) Elongated apex of the ovary (style).
(c) The tip of the style (stigma).
Fusion of Carpels
1. Apocarpous : The carpels present on the thalamus remain free.
2. Sub-apocarpous : The carpels present inside the ovary are partly fused and partly free.
Syncarpous ovary : The carpels of the gynoecium are fused in single structure.
The ovary consists of one or more ovules. On the placenta, the arrangement of ovules is called ‘placentation’. Placentation are of seven types.
1. Marginal placentation.
2. Parietal placentation.
3. Axile placentation.
4. Free central placentation.
5. Basal placentation.
6. Apical or Pendulous placentation.
7. Superficial placentation.
Style : Style develops from the gynoecium. It is an elongated tubular, stalk like structure. Style is of three types—
(i) Terminal style : It develops from the apical part of the ovary, e.g. Hibiscus.
(ii) Lateral style : It develops from the lateral side of the ovary, e.g. Mangifera.
(iii) Gynobasic style : It arises from the base of the ovary, e.g. Ocimum.
Stigma : Terminal part of the style which receives pollen grains at the time of pollination.
1. Capitate : Stigma is round or gap-like, e.g. Citrus.
2. Plumose : Stigma is feather like, e.g. Oryza.
3. Bifid : Forked stigma, e.g. Tridax.
4. Dumb-bell shaped : Stigma is dumb-bell shaped, e.g. Catheranthus.
5. Discoid : Stigma is disc like, e.g. Melia.
6. Funnel shaped : Stigma is funnel like. e.g. Crocus.
7. Linear : Narrow and long stigma, e.g. Acacia.
8. Radiate hook like : Stigma is hook like. e.g. Papaver.
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