Morphology Of The Flower

Morphology Of The Flower

Flower is highly modified reproductive shoot. A typical flower consists of four distinct circles of whorls of floral leaves, the calyx, corolla, androecium and gynoecium, arranged on the thalamus. The calyx comprises of usually green floral leaves, the sepals and forms the outermost protective whorl. The corolla comprises of variously coloured floral leaves, the petals presents inner to the calyx. The petals attract the insects and animals for pollination. The calyx and corolla are collectively and termed as perianth. The androecium is formed of modified sporophylls, the stamens, in which microspores or pollen grains are produced. The innermost whorl gynoecium also called pistil consists of modified megasorophylls, the carpels, which contain integuments megasporangia, the ovules.

Presence or Absence of Bracts:

A bract is a special leaf that bears a flower or a cluster of flower in its axils or completely encloses a group of flowers.

A bract may be:

Leafy Bract: When it is green and like ordinary leaf.

Scaly Bract: If the bract is small, thin and scale-like.

Petaloid: When the bracts are coloured like petals as in Euphorbia, Bougainvillea.

Involucre: A group of bracts forming a cup-like structures at the base of the inflorescence, e.g., in sunflower.

Glumes: These are small dry bracts found in wheat.

Spathe: A large bract enclosing a cluster of flower.

In terms of presence or absence of a bract, a flower may be:

Bracteate: If the flower is present in the axil of bract, e.g., in Solanum, Petunia.

Bracteoles:

Sometimes secondary bracts are present on the pedicel of a flower or just below the calyx. These are called bracteoles. In some cases, they form a whorl called epicalyx, e.g., in Hibiscus rosa-sinensis (China rose). If the bracteoles are present, the flower is said to be bracteolate.

Attachment of Flower:

The flower may be attached to the floral axis directly or through a stalk, the pedicel.

Therefore, it may be

Pedicellate: When the flower is attached to the floral axis through pedicel, e.g., Rosa.

Sessile: When the pedicel is absent and the flower is attached to floral axis directly.

Sub-sessile: In some cases, a very small pedicel is present, e.g., in Althea rosea.

Presence or Absence of Floral Whorls:

With reference to presence or absence of floral whorls a flower may be:

Complete: If all the florals whorls, i.e., calyx, corolla, androecium and gynoecium are present in a flower, e.g., in Solanum, Hibiscus.

Incomplete: If any one or more of the floral leaves is missing, e.g., in Euphorbia, Luffa, Cucurbita.

Presence or Absence of Reproductive Whorls:

With reference to presence or absence of reproductive whorls a flower may be:

Perfect: When both the reproductive floral leaves, the stamens and carpels are present. A perfect flower is bisexual or hermaphrodite.

Imperfect: If any one of the reproductive floral leaves, either stamens or carpels may be absent. An imperfect flower is always unisexual. A unisexual flower may be; (a) Staminate, when it contains stamens only; (b) Pistillate, when it contains carpels only.

Symmetry of the Flower:

Symmetry refers to whether a flower can be divided into equal halves or not. If a flower can be divided into two equal halves it is called symmetrical, and if not asymmetrical.

A symmetrical flower may be:

Actinomorphic: When the flower can be divided into equal halves in more halve in more than one plane, e.g., in Petunia, Poppy, etc. An actinomorphic flower is also called regular.

Zygomorphic: When the flower can be divided into equal halves in one plane only, e.g., in Lathyrus, Ocimum, etc. A zygomorphic flower is also called irregular.

Position of the Floral Leaves on Receptacle:

The arrangement of floral leaves on thalamus is called insertion. Three types of insertions are recognized on the basis of shape of thalamus and position of gynoecium to other floral parts. These are:

Hypogynous: In this case the thalamus is convex and gynoecium develops at the top of the thalamus., while all other floral leaves develop below the point of attachment of gynoecium, for example in Ranunculus, Brassica, etc.

Perigynous: The thalamus is flattened and in the form of a circular disc. The gynoecium is present in the centre of the disc while the stamens, petals and sepals are arranged around the gynoecium, e.g., in Prunus, In Rosa the margins of the thalamus grows upward and it becomes cup-shaped so that the stamens, petals and sepals come to lie at the margins of the cup above the carpels.

Epigynous: In this case the thalamus is cup-shaped and becomes fused with ovary. The stamens, petals, sepals are attach above the level of the ovary, e.g., in Malus (apple).

Calyx

The calyx is the outermost whorl of flower consisting of sepals.

Caducous: The sepal fall off as the flower open as in poppy.

Decedious: The sepal falls off as the flower withers as in buttercup.

Persistent: The sepal remains in place as the fruit developed as in Solanaceae.

Petaloid: Sepals are coloured like the petals. As in larkspur.

Polysepalous: The sepals are free from one another.

Gamosepalous: The sepals are united partially or completely as in Citrus.

Cohesion of Sepals:

The sepals may be united to each other partially or completely or free from one another. According to the cohesion the calyx may be:

Polysepalous: When the sepals are free from one another. If we pull a sepal, the others are not pulled along with it. In Brasssica (sarson).

Gamosepalous: When the sepals are fused to each other. If we pull a sepal all will be pulled, e.g., in Lathyrus (pea), Rosa (rose), etc.

Shape of Calyx:

The fusion of sepals results in various shapes of corolla, such as:

Tubular: The sepals are fused to form a tube-like structure, e.g., in Verbena.

Campanulate: The sepals unite to form a bell-shaped structure, e.g., in Atropa belladonna.

Pappus: In Helianthus annus (sunflower), the sepals are much reduced and are represented by hairs forming a structure, the pappus.

Bilabiate: In members of labiatae such as Salyia and Ocimum (niazbo), the sepals fuse to form a bilipped structure.

Spurred: In Delphinium (larkspur) one or more sepals form a long hollow tube, the spur. It projects downwards and contains nectaries.

Hooded: One or more sepals are modified into hood like structures, as in monk hood.

Colours of Sepals:

The sepals are green usually, but in some cases, they may be coloured like petals. Such corolla is called petaloid, e.g., in Delphinium ajacis (larkspur).

Position of Sepals on Receptacles:

The sepals may be inferior or superior according to their position on the thalamus.

Inferior: When the sepals are attached below the level of ovary they are called inferior sepals.

Superior: When the sepals are attached above the level of ovary they are called superior sepals.

 

Corolla

It is the second whorl of flower inner to calyx. It comprises of coloured floral leaves known as petals.

Caducous: The petals fall of as the flower opens as in grape.

Sepaloid: Petals are green like the sepals. As in Uvaria.

Polysepalous: The petals are free from one another. As in Brassica.

Gamosepalous: The petals are united partially or completely as in sunflower.

Number of Petals:

The petals may be arranged in a single whorl (Brassica) or many whorls (Rosa). The number of petals per whorl is counted and recorded. However, if the number of petals is many, the term infinite may be used.

Cohesion of Petals:

According to the mode of cohesion of petals, the corolla may be:

Polypetalous: When the petals are free from one another, e.g., in Ranunculus (buttercup), Brassica (sarson), etc.

Gamopetalous: When all are few petals in corolla are united each other, e.g., in Latyrus (garden pea), Delphinium (larkspur), Petunia, etc.

Shape of Corolla:

The arrangement of both free and fused petals results in different shapes of the corolla such as:

Ungiculate or Clawed: The petals are narrow at the base (claw) while the upper portion is broad (limb), e.g., in Brassica napa (turnip), The petals are free.

Caryphyllaceous: The corolla is tube-like and consists of five free petals. Each petal has a long claw and the limbs are spread out above the tube at right angles to the claws, e.g., in Dianthus.

Cruciform: In members of Brassicaceae (Cruciferae), the corolla consists of four free petals arranged in the form of a cross.

Rosaceous: The corolla consists of five free petals. The petals have very short claws and the limbs spread irregularly outwardly, e.g., in Rosa.

Papilionaceous: The corolla comprises of five petals, of which three are free and two are fused. The posterior petal is large and is called standard; on either side of standard there are two small petals, the wings; and within the wings there is a boat-shaped structure formed of two fused petals, the keel. Thus, the corolla assumes butterfly shape. This corolla is characteristics of members of family Papilionaceae.

Bilabiate: The petals fuse to form a bilipped structure, if the lips gap apart, the corolla is bilabiate ringent, e.g., in Salvia, Ocimum, etc; and if the lips meet each other as a closed mouth, the corolla is called bilabiate personate, e.g., in Antirrhinum. Bilabiate corolla is characteristic of family Lamiaceae (Labiatae).

Spurred: In this type of corolla two or more petals unite and prolong into a tubular structure, the spur, e.g., in Delphinium (larkspur).

Tubular: The petals unite form a tube in the lower portion and a long, flattened strap-like upper portion, e.g., in ray-florets of Helianthus annus (sunflower).

Rotate: The corolla is wheel-shaped. The lower part of the petals is united while the upper parts spread out like spokes of wheel, e.g., in Solanum nigrum (mako).

Campanulate: The petals fuse to form a bell-shaped corolla, e.g., in Withania sominifera.

Colour of Petals:

The petals are various coloured, however in some cases, these may be green like sepals. In this case, these are called sepaloid, e.g., Delphinium (larkspur).

Position of Petals on Receptacle:

The petals may be inferior or superior according to their position on the thalamus.

Inferior: When the petals are attached below the level of ovary they are called inferior petals.

Superior: When the petals are attached above the level of ovary they are called superior petals.

Androecium

It is the first of two reproductive whorls of flowers present next to corolla. It comprises of stamens. Each stamen consists of a stalk, the filament; and a bilobed structure at the top of the filament, the anther. The anther lobes are joined to each other through a tissue, the connective. In some species, the stamens are reduced and sterile, i.e., do not produce pollens. Such stamens are called staminodes, e.g., in Canna indica.

Number of Stamens:

The number of stamens is fixed for a species. The androecium may comprise of one, two or more stamens. All these stamens present free from each other. Thus, according to the number of stamens, the androecium may be:

Monanadrous: When it comprises of a single stamen only.

Diandrous: When the androecium consists of two stamens.

Tri, Tetra- and Pentandrous: When the stamens in the androecium are three, four or five, respectively.

Polyandrous: If the number of stamens in an androecium is many.

Length of Stamens:

The stamens of flowers may be of same length or there may vary relation to each other, i.e., stamens may be short or long. Thus, on the basis of the length of stamens, the androecium may be:

Didynamous: The stamens in androecium are four in number, two long and two short and arranged in a single whorl, e.g., in Ocimum (niazbo).

Tetradynamous: The stamens in androecium are six in number, four long and two short, and arranged into two whorls, e.g., in Brassica (sarson).

Adhesion of Stamens:

In many flowers, the stamens adhere to petals, perianth or carpels. These conditions are known as:

Epipetalous: When the stamens are fused to petals, e.g., in Solanum and Ocimum (niazbo).

Epiphyllous: The stamens adhere to perianth leaves, e.g., in Asphodelus (piazi).

Gynandrous: In this case, the stamens are fused with gynoecium, e.g., in Calotropis.

Cohesion of Filaments and Anthers:

The stamens occur singly free from one another usually. However, in some cases their filaments unite to form one are more bundles while the stamens are free (adelphous). In other cases, the anthers become united and filaments remain free (syngenesious); and in still other cases both filament and anthers unite to form a group (synadrous). Therefore, the cohesion of filaments and anthers may be:

Monoadelphous: When the stamens unite by their filaments to form a single group, e.g., in Hibiscus rosa-sinensis (China rose), Althaea rosea (gul-e-khaira), etc.

Diadelphous: When the stamens unite by their filaments and form two bundles, e.g., in Lathyrus (garden pea).

Polyadelphous: When the stamens unite by their filaments and form more than two bundles, e.g., in Citrus (lemon), Ricinus communis (castor-oil), etc.

Syngenesious: In this case, the stamens unite by their anthers while the filaments remain free, e.g., in Heliantus annus (sunflower).

Synandrous: The condition when stamens unite both by their filaments and anthers, e.g., in Cucurbita (gourd).

Attachment of Filament to Anther:

The way filament of a stamen is attached to its anther may be:

Basifixed: When the filament is attached to the base of the anther, e.g., in Brassica (sarson), Cassia fistula (amaltas), etc.

Adnate: In this case, the filament runs whole length of the anther from base to the apex, e.g., in Ranunculus (Buttercup).

Dorsifixed: In this type the filament is attached to the back of the anther, e.g., in Bauhinia variegata (kachnar).

Versatile: When the filament is attached to the back of the anther at a point only so that the anther can swing freely, e.g., in members of Graminae.

Elongated: In this type, the elongated connective separate the upper fertile anther lobe from lower sterile one, e.g., in Salvia.

Introse: When the anthers face inward, e.g., in Solanum (mako), Hibiscus rosa-sinensis (China rose).

Position of Stamens on Thalamus:

The stamens may be:

Inferior: When they are inserted below the level of the ovary. In hypogynous and perigynous flower the stamens are inferior.

Superior: When the stamens are inserted above the level of the ovary. In epigynous flower the stamens are superior.

Gynoecium

Gynoecium is the innermost whorl of flower consisting of carpels. It occupies the centre of the thalamus usually, it is also called a pistil. A carpel is considered to be a modified folded leaf. The two edges of the leaf meet and fuse together. The fuse margin is called ventral suture, While the line corresponding the midrib of the leaf is called the dorsal suture. Each carpel consists of a basal swollen part, the ovary; a stalk present at the top of the ovary, the style; and the tip of the style, the stigma. The ovary contains ovules.

Numbers of Carpels:

A gynoecium or pistil may consist of one or more carpels therefore it may be:

Monocarpellary or Simple: When the pistil comprises of a single carpel, e.g., in Lathyrus (garden pea).

Polycarpellary or Compound: When the pistil consists of two or more carpels, e.g., in Brassica.

A compound pistil may be:

Bicarpellary: When the pistil comprises of two carpels, may be free from each other or united, e.g., in Calotropis (free) and Brassica (united).

Tricarpellary: When the pistil comprises of three carpels, may be free from each other or united, e.g., in Aconitum (free) and Euphorbia (united).

Tetracarpellary: When the pistil consists of four free or united carpels, e.g., in Datura.

Pentacarpellary: When the pistil comprises of free or united five carpels, e.g., in Hibiscus rosa-sinensis (China rose).

Cohesion of Carpels:

A compound or polycarpellary pistil may be:

Apocarpous: When the carpels are free from each other, e.g., in Ranunculus.

Syncarpous: When the carpels are united, e.g., in Euporbia.

In a syncarpous pistil:

The ovaries may be united but the style and stigma are free, e.g., in Malva.

The ovaries and style are united, but the stigmas are free, e.g., in Hibiscus rose-sinensis and Helianthus annus.

The ovaries free and styles and stigmas are united, e.g., in Nerium.

The ovaries and styles are free, but the stigmas are united, e.g., in Calotropis (Ak).

Monocarpellary:

When the gynoecium consists of single carpel as in Cassia.

Bicarpellary:

When the gynoecium consists of two carpels as in Brassica, potato, etc.

Tricarpellary:

When the gynoecium consists of three carpels as in Tomato.

Polycarpellary:

When the gynoecium consists of many carpels as in Citrus.

Number of Locules:

The ovary may be divided into chambers called locules. There may be a single locule or two or more than two locules in an ovary. Thus, on the basis of number of locules ovary may be:

Unilocular: When the ovary consists of a single locule, e.g., in Delphinium (larkspur).

Bilocular: When the ovary contains two locules, e.g., in Solanum (mako).

Trilocular: In this case, the ovary comprises of three chambers, e.g., in Asphodelus.

Tetralocular: In this case the ovary consists of four locules, e.g., in Ocimum (niazbo).

Pentalocular: When the ovary contains five locules, e.g., in Hibiscus rosa-sinensis.

Multilocular: When the ovary comprises of many locules, e.g., in Citrus.

Placentation:

The ovules are borne on cusion-like ridges, the placentation that arises from the wall is called placentation. The placentation may be:

Marginal: In this type the ovary is simple (monocarpellary) and unilocular, and the placentae develop along the fused margins of the carpel, i.e., along the ventral suture, for example in Lathyrus (garden pea), Cassia fistula (amaltas).

Axile: The gynoecium is polycarpellary and syncarpous. The margins of the carpels move inward and meet in the centre of the ovary to form a central or axile column, so that the ovary becomes multilocular. The placentae develop along the axile column, e.g., in Euphorbia, Hibiscus, etc.

Free Central: The ovary is compound and unilocular. A central axis arises from the base of ovary and placentae develop along the axis, e.g., in Dianthus and Stellaria.

Parietal: The ovary is compound and unilocula. They fused margins of the carpels swell up to form placentae, e.g., in Brassica, Cucumber, etc.

Basal: The ovary is compound and unilocular and usually a single large ovule arises is attached to the base of the ovary, e.g., in member of Composiate (Helianthus).

Superficial: The ovary is compound and multilocuar. The placentae develop all along the inner surface of the partition wall, e.g., in Nymphea.

Types of Style:

The style may be:

Terminal: If the style arises from the top of the ovary, e.g., in Brassica.

Lateral: If the style arises from side of the ovary, e.g., in strawberry.

Gynobasic: When the style arises between the lobes of ovary from its base, e.g., in Ocimum, Salvia.

Petaloid: When the style is coloured like petals, e.g., in Canna.

Number and Shape of Stigma:

The stigma may be:

Capitate: When is rounded and knob-like. It is common type of stigma.

Branched: In this case, the stigma is branched. It may be: bifid – if two branches are present (Helianthus), or trifid – if three branches are present.

Feathery: When the stigma bears hairs, e.g., in members of Poaceae (grasses).

Linear: When the stigma is long and narrow.

Position of the Ovary on Thalamus:

The ovary may be:

Superior: When the ovary is inserted above the level of other floral leaves, e.g., in Brassica. In hypoynous and perigynous flowers the ovary is superior.

Inferior: When the ovary is inserted below the level of other floral leaves, e.g., in Coriandrum. In epigynous flowers the ovary is inferior.