Prasanna

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Concept of Species – Morphological, Biological and Phylogenetic

Species is the fundamental unit of taxonomic classification. Species is a group of individual organisms which have the following characters.

1. A population of organisms which closely resemble each other more than the other population.
2. They descend from a common ancestor.
3. In sexually reproducing organisms, they interbreed freely in nature, producing fertile offspring.

Species concepts can be classified into two general groups. Concept emphasizing process of evolution that maintains the species as a unit and that can result in evolutionary divergence and speciation. Another concept emphasises the product of evolution in defining a species.

Types of Species

There are different types of species and they are as follows:

1. Process of evolution – Biological Species
2. Product of evolution – Morphological Species and Phylogenetic Species

Morphological Species (Taxonomic Species)

When the individuals are similar to one another in one or more features and different from other such groups, they are called morphological species.

Biological Species (Isolation Species)

According to Ernest Mayr 1963,“ these are groups of populations that interbreed and are reproductively isolated from other such groups in nature”.

Phylogenetic Species

This concept was developed by Meglitsch (1954), Simpson (1961) and Wiley (1978). Wiley defined phylogenetic species as “an evolutionary species is a single lineage of ancestor descendent populations which maintains its identity from other such lineages which has its own evolutionary tendencies and historical fate”.

Phenetic Species Concept (morphological species concept): a set of organisms that look similar to each other and is distinct from other sets. Phylogenetic Species concept: the smallest monophyletic group distinguishable by shared derived (synapomorphic) characteristics.

A species concept is a way of defining or at least thinking about the differences between two species, especially otherwise quite similar species, and the Morphological Species Concept involves thinking about these differences in terms of how species differ in the shapes of their bodies and otherwise what they look.

The concept of species is an important but difficult one in biology, and is sometimes referred to the “species problem”. Some major species concepts are: Typological (or Essentialist, Morphological, Phenetic) species concept. Typology is based on morphology/phenotype.

The phylogenetic species concept has two distinct advantages:

1. It can be applied to any population (fossil, asexual, or sexual)
2. It is logical because different species have different synapomorphies only if they are isolated from gene flow and have evolved independently.

The biological species concept relies on behavioral data and emphasizes reproductive isolation between groups. The lineage species concept relies on genetic data and emphasizes distinct evolutionary trajectories between groups, which result in distinct lineages (branches on a phylogenetic tree).

According to the most widely used species definition, the biological species concept, a species is a group of organisms that can potentially interbreed, or mate, with one another to produce viable, fertile offspring. For example, when a female horse and a male donkey mate, they produce hybrid offspring called mules.

Evolution is a gradual change in the inherited traits of a population over many generations. Natural selection is a mechanism where the members of a population best suited to their environment have the best chance of surviving to pass on their genes.

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Taxonomy and Systematics

The word taxonomy is derived from Greek words “taxis” (arrangement) and “nomos” (rules or laws). Taxonomy is defined as as“the science dealing with the study of classification including the bases, principles, rules and procedures”.

Simpson (1961) defined Systematics as, “Scientific study of the kinds and diversity of organisms and all relationships among them”. Though there are two terms are used in an interchangeable way, they differ from each other.

Differences Between Taxonomy and Systematics

Taxonomy	Systematics
1. Discipline of classifying organisms into taxa.	1. Broad field of biology that studies the diversification of species.
2. Governs the practices of naming, describing, identifying and specimen preservation.	2. Governs the evolutionary history and phylogenetic relationship in addition to taxonomy.
3. Classification + Nomenclature = Taxonomy	3. Taxonomy + Phylogeny = Systematics

Species
Species is the lowest of classification and shows the high level of similarities among the organisms. For example, Helianthus annuus and Helianthus tuberosus. These two species differ in their morphology. Both of them are herbs but Helianthus tuberosus is a perennial herb.

Genus
Genus consists of multiple species which have similar characters but differ from the species of another genus. Example: Helianthus, Tridax.

Family
Family comprises a number of genera which share some similarities among them. Example: Asteraceae.

Order
Order includes group of families which show less similarities among them.

Class
Class consists of group of orders which share few similarities.

Division
Division is the next level of classification that consists of number of classes. Example: Magnoliophyta.

The main difference between taxonomy and systematics is that taxonomy is involved in the classification and naming of organisms whereas systematics is involved in the determination of evolutionary relationships of organisms. This means systematics ascertain the sharing of the common ancestry by different organisms.

Systematics may be defined as the study of the kinds and diversity of organisms and the relationships among them. Taxonomy, on the other hand, is the theory and practice of identifying, describing, naming, and classifying organisms.

Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Systematics, in other words, is used to understand the evolutionary history of life on Earth.

Systematics plays a central role in biology by providing the means for characterizing the organisms that we study. Through the production of classifications that reflect evolutionary relationships it also allows predictions and testable hypotheses.

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Seed Various Types and its Significance

Do all fruits contain seeds? No, triploid fruits do not. The seed is a fertilized mature ovule which possess an embryonic plant, usually stores food material and has a protective coat. After fertilization, changes occur in various parts of the ovule and transforms into a seed.

Types of Seed

I. Based on the number of cotyledons two types of seeds are recognized.

(i) Dicotyledonous Seed:
Seed with two cotyledons.

(ii) Monocotyledonous Seed:
Seed with one cotyledon.

II. Based on the presence or absence of the endosperm the seed is of two types.

(i) Albuminous or Endospermous Seed:
The cotyledons are thin, membranous and mature seeds have endosperm persistent and nourishes the seedling during its early development. Example: Castor, sunflower, maize.

(ii) Ex-albuminous or Nonendospermous Seed:
Food is utilized by the developing embryo and so the mature seeds are without endosperm. In such seeds, colyledons store food and become thick and fleshy. Example: Pea, groundnut.

Significance of Seeds:

1. The seed encloses and protects the embryo for next generation.
2. It contains food for the development of embryo.
3. It is a means for the dispersal of new individuals of the species.
4. A seed is a means for perpetuation of the species. It may lie dormant during unfavorable conditions but germinates on getting suitable conditions.
5. Seeds of various plants are used as food, both for animals and men.
6. They are the basis of agriculture.
7. Seeds are the products of sexual reproduction so they provide genetic variation and recombination in a plant.
   

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Fruits – Structure of Fruits and its Types

We know about several kinds of fruits, but by botanical study we will be surprised to know the types of fruits and how they are produced by plants. Fruits are the products of pollination and fertilization, usually containing seeds inside.

In common person’s perspective a fruit may be defined as an edible product of the entire gynoecium and any floral part which is sweet, juicy or fleshy, coloured, aromatic and enclosing seeds. However the fruit is a fertilized and ripened ovary. The branch of horticulture that deals with the study of fruits and their cultivation is called pomology.

Structure of Fruit

Fruit has a fruit wall. It is otherwise called pericarp. It is differentiated into outer epicarp, middle mesocarp and inner endocarp. The inner part of the fruit is occupied by the seed.

Types of Fruit

Fruits are classified into three types:

Simple Fruits
The fruits are derived from a single ovary of a flower Example: Mango, Tomato. Simple fruits are classified based on the nature of pericarp as follows.

A. Fleshy Fruit

The fruits are derived from single pistil where the pericarp is fleshy, succulent and diffrentiated into epicarp, mesocarp and endocarp. It is subdivided into the following.

(a) Berry:
Fruit develops from bicarpellary or multicarpellary, syncarpous ovary. Here the epicarp is thin, the mesocarp and endocarp remain undifferentiated. They form a pulp in which the seeds are embedded. Example: Tomato, Grapes, Brinjal.

(b) Drupe:
Fruit develops from monocarpellary, superior ovary. It is usually one seeded. Pericarp is differentiated into outer skinny epicarp, fleshy and pulpy mesocarp and hard and stony endocarp around the seed. Example: Mango, Coconut.

(c) Pepo:
Fruit develops from tricarpellary inferior ovary. Pericarp turns leathery or woody which encloses, fleshy mesocarp and smooth endocarp. Example: Cucumber, Watermelon, Bottle gourd, Pumpkin.

(d) Hesperidium:
Fruit develops from multicarpellary, multilocular, syncarpous, superior ovary. The fruit wall is differentiated into leathery epicarp with oil glands, a middle firous mesocarp. The endocarp forms distinct chambers, containing juicy hairs. Example: Orange, Lemon.

(e) Pome:
It develops from multicarpellary, syncarpous, inferior ovary. The receptacle also develops along with the ovary and becomes fleshy, enclosing the true fruit. In pome the epicarp is thin skin like and endocarp is cartilagenous. Example: Apple, Pear.

(f) Balausta:
A fleshy indehiscent fruit developing from multicarpellary, multilocular inferior ovary whose pericarp is tough and leathery. Seeds are attached irregularly with testa being the edible portion. Example: Pomegranate.

B. Dry Fruit

They develop from single ovary where the pericarp is dry and not differentiated into epicarp, mesocarp and endocarp. It is further subdivided into three types.

1. Dry Dehiscent Fruit

Pericarp is dry and splits open along the sutures to liberate seeds. They can be classified into following types.

(a) Follicle:
Fruit develops from monocarpellary, superior ovary and dehisces along one suture. Example: Calotropis.

(b) Legume or Pod:
Fruit develops from monocarpellary, superior ovary and dehisces through both dorsal and ventral sutures. Example: Pisum.

(c) Siliqua:
Fruit develops from bicarpellary, syncarpous, superior ovary initially one chambered but subsequently becomes two chambered due to the formation of false septum (replum). The fruit dehisces along two suture. Example: Brassica.

(d) Silicula:
Fruit similar to siliqua but shorter and broader. Example: Capsella.

(e) Capsule:
Fruit develops from multicarpellary, syncarpous, superior ovary. Based on the dehiscence pattern they are divided into.

(i) Septicidal:
Capsule splitting along septa and valves remaining attached to septa. Example: Aristolochia.

(ii) Loculicidal:
Capsule splitting along locules and valves remaining attached to septa. Example: Abelmoschus.

(iii) Poricidal:
Dehiscence through terminal pores. Example: Papaver.

2. Dry Indehiscent Fruit

Dry fruit which does not split open at maturity. It is subdivided into.

(a) Achene:
Single seeded dry fruit developing from single carpel with superior ovary. Achenes commonly develop from apocarpous pistil, Fruit wall is free from seed coat. Example: Clematis, Delphinium.

(b) Cypsela:
Single seeded dry fruit, develops from bicarpellary, syncarpous, inferior ovary with reduced scales, hairy or feathery calyx lobes. Example: Tridax.

(c) Caryopsis:
It is a one seeded fruit which develops from a monocarpellary, superior ovary. Pericarp is inseparably fused with seed. Example: Oryza.

(d) Nut:
They develop from mulicarpellary, syncarpous, superior ovary with hard, woody or bony pericap. It is a one seeded fruit. Example: Anacardium.

(e) Samara:
A dry indehiscent, one seeded fruit in which the pericarp devlops into thin winged structure around the fruit. Example: Acer.

(f) Utricle:
They develop from bicarpellary, unilocular, syncarpus, superior ovary with pericarp loosely enclosing the seeds. Example: Chenopodium.

3. Schizocarpic Fruit

This fruit type is intermediate between dehiscent and indehiscent fruit. The fruit instead of dehiscing, splits into number of segments, each containing one or more seeds. They are of following types.

(a) Cremocarp:
Fruit develops from bicarpellary, syncarpous, inferior ovary and splitting into two one seeded segments known as mericarps. Example: Coriander.

(b) Carcerulus:
Fruit develops from bicarpellary, syncarpous, superior ovary and splitting into four one seeded segments known as nutlets. Example: Leucas.

(c) Lomentum:
The fruit is derived from monocarpellary, unilocular ovary. A leguminous fruit, constricted between the seeds to form a number of one seeded compartments that separate at maturity. Example: Mimosa.

(d) Regma:
They develop from tricarpellary, syncarpous, superior, trilocular ovary and splits into one­seeded cocci which remain attached to carpophore. Example: Ricinus.

Aggregate Fruits

Aggregate fruits develop from a single flower having an apocarpous pistil each of the free carpel develops into a simple fruitlet. A collection of simple fruitlets makes an Aggregate fruit. An individual ovary develops into a drupe, achene, follicle or berry. An aggregate of these fruits borne by a single flower is known as an etaerio. Example: Annona, Polyalthia.

Multiple or Composite Fruit:
A Multiple or composite fruit develops from the whole inflorescence along with its peduncle on which they are borne.

(a) Sorosis:
A fleshy multiple fruit which develops from a spike or spadix. The flowers fused together by their succulent perianth and at the same time the axis bearing them become fleshy or juicy and the whole inflorescence forms a compact mass. Example: Pine apple, Jack fruit.

(b) Syconus:
A multiple fruit which develops from hypanthodium inflorescence. The receptacle develops further and converts into fleshy fruit which encloses a number of true fruit or achenes which develops from female flower of hypanthodium inflorescence. Example: Ficus

Functions of Fruit

• Edible part of the fruit is a source of food and gives energy for animals.
• They are source of many chemicals like sugar, pectin, organic acids, vitamins and minerals.
• The fruit protects the seeds from unfavourable climatic conditions and animals.
• Both fleshy and dry fruits help in the dispersal of seeds to distant places.
• In certain cases, fruit may provide nutrition to the developing seedling.
• Fruits provide source of medicine to human.

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Construction of Floral Diagram and Floral Formula

A floral formula is a simple way to explain the salient features of a flower. The floral diagram is a representation of the cross section of the flower. It represents floral whorls arranged as viewed from above. Floral diagram shows the number and arrangement of bract, bracteoles and floral parts, fusion, overlapping and placentation. The branch that bears the flower is called mother axis.

The side of the flower facing the mother axis is called posterior side. The side facing the bract is the anterior side. The members of different floral whorls are shown arranged in concentric rings.

Br: Bracteate
Ebr: Ebracteate
Brl: Bracteolate
Ebrl: Ebracteolate
⊕: Actinomorphic
%: Zygomorphic

K: Calyx, K₅ five sepals, aposepalous, K(₅) five sepals synsepalous.
C: Corolla, C₅ five petals, apopetalous, C(₅) five petals sympetalous C(₂₊₃) corolla bilabiate with upper lib two lobes.
A: Androecium A₃ three stamens free, A₂₊₂, Stamens 4, two whorls (didynamous) each whorl two stamens (free)

A₍₉₎₊₁ 
Stamens ten, two bundles (diadelphous) 9 stamens unite to form one bundle, 1 stamen form another bundle.

Epipetalous represented by an arc.

A⁰: Staminode(sterile stamen)
G. Gynoecium or pistil – G₂ – Carpels two, free (apocarpous)
G₍₃₎ – Carpels three, united (syncarpous)
G₀ – Pistillode (sterile carpel)

\(\underline{G}\) – Superior Ovary
G inferior Ovary
G- – Semi-inferior ovary
∞ – Indefinite number of units

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Gynoecium – Definition, Types and its Structure

Gynoecium or pistil is the female reproductive part of the flower. A pistil consists of an expanded basal portion called the ovary, an elongated section called a style and an apical structure that receives pollen called a stigma. Ovary with stipe is called stipitate ovary.

Carpel:
They are components of a gynoecium. Gynoecium is made of one or more carpels. Carpels may be distinct or connate.

Number of Carpel

Fusion of Carpels

It is an important systematic character. Apocarpous gynoecium is generally thought to be ancestral condition in Angiosperms.

Number of Locules

Ovary bears ovules on a specialized tissue called placenta. A septum is a crosswall or partition of ovary. The walls of ovary and septa form a cavity called locule. Like that tetralocular and pentalocular ovaries are present according to the locule numbers four or fie. More than one locule ovaries are called plurilocular.

Extension of the Condensed Internode of the Receptacle

1. Anthophore:
The internodal elongation between calyx and corolla. Example: caryophyllaceae (Silene conoidea)

2. Androphore:
The internodal elongation between the corolla and androecium. Example: Grewia.

3. Gynophore:
The internodal elongation between androecium and gynoecium. Example: Capparis.

4. Gynandrophore or Androgynophore:
The unified internodal elongation between corolla and androecium and androecium and gynoecium. Example: Gynandropsis.

Ovary Position

The position or attachment of ovary relative to the other floral parts. It may be classified into

1. Superior Ovary:
It is the ovary with the sepals, petals and stamens attached at the base of the ovary.

2. Inferior Ovary:
It is the ovary with the sepals, petals and stamens attached at the apex of the ovary.

3. Half-inferior Ovary:
It is the ovary with the sepals, petals and stamens or hypanthium attached near the middle of the ovary.

Perianth/Androecial Position on Thalamus:
It describes placement of the perianth and androecium relative to the ovary and to a hypanthium, if present (Figure 4.25).

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Androecium – Definiton of Androecium and its Various Types

Androecium:
Third whorl of flower is the male reproductive part of the flower. It is composed of stamens (microsporophylls).

Each Stamen consist of 3 parts:

• Filament
• Anther
• Connective

Anther:
Upper swollen part with microsporangia.

Filament:
Stalk of stamen

Connective:
Tissue connecting anther lobes with filament

Anther typically contains two compartments called thecae (singular theca). Each theca consists of two microsporangia. Two microsporangia fused to form a locule. Sterile stamens are called Staminodes. Example: Cassia. Distinct: stamens which do not fuse to one another. Free: stamens which do not fuse with other parts of flower. Apostemonous: flowers with stamens that are free and distinct.

Fusion of Stamens:
The fusion of stamens fusing among themselves or with other parts of flower. They are of two types.

• Connation and
• Adnation

1. Connation:
Refers to the fusion of stamens among themselves. It is of 3 types:-

• Adelphy
• Syngenecious
• Synandrous

Adelphy:
Filaments connate into one or more bundles but anthers are free. It may be the following types.

(i) Monadelphous:
Filaments of stamens connate into a single bundle. Example: Malvaceae (Chinarose, Cotton).

(ii) Diadelphous:
Filaments of stamens connate into two bundles. Example: Fabaceae (pea) and Clitoria.

(iii) Polyadelphous:
Filaments connate into many bundles. Example: Citrus, Bombax

Syngenesious:
Anthers connate, filaments free. Example: Asteraceae.

Synandrous:
Filaments and anthers are completely fused. Example: Coccinea.

2. Adnation:
Refers to the fusion of stamens with other flral parts. Epipetalous: Stamens are adnate to petals. Example: Brinjal, Datura.

a. Episepalous:
Stamens are adnate to sepals. Example: Grevillea (Silver oak)

b. Epitepalous (Epiphyllous):
Stamens are adnate to tepals. Example: Asparagus.

c. Gynostegium:
Connation product of stamens and stigma is called gynostegium. Example: Calotropis and Orchidaceae.

d. Pollinium:
Pollen grains are fused together as a single mass Example: Calotropis

Arrangement of stamens relate to length of stamens:

1. Didynamous:
Four stamens of which two with long fiaments and two with short filaments. Example: Ocimum

2. Tetradynamous:
Six stamens of which four with long filaments and two with short filaments. Example: Brassica.

3. Heterostemonous:
Stamens are of different lengths in the same flower. Example: Cassia.

Anther Types

1. Monothecal:
One lobe with two microsporangia. They are kidney shaped in a cross section. Example: Malvaceae

2. Dithecal:
It is a typical type, having two lobes with four microsporangia. They are butterfly shaped in cross section. Example: Solanaceae.

Anther Attachment

1. Basifixed:
(Innate) Base of anther is attached to the tip of filament. Example: Datura.

2. Dorsifixed:
Apex of filament is attached to the dorsal side of the anther. Example: Hibiscus.

3. Versatile:
Filament is attached to the anther at midpoint. Example: Grasses.

4. Adnate:
Filament is continued from the base to the apex of anther. Example: Nelumbo

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Accessory Organs – Everything You Need to Know

Arrangement of Whorls

The position of perianth (sepals, petals, tepals) parts relative to one another is called perianth arrangement.

1. Cyclic or Whorled:
All the floral parts are arranged in definite whorls. Example: Brassica.

2. Acyclic or Spiral:
The floral parts are arranged in spirals on the elongated fleshy torus. Example: Magnolia.

3. Spirocyclic or Hemicyclic:
Some parts are in whorls and others parts are in spirals. Example: Annona, Polyalthia

Calyx

Calyx protects the flower in bud stage. Outermost whorl of flower is calyx. Unit of calyx is sepal. Normally green in colour.

1. Fusion:

a. Aposepalous (Polysepalous):
The flower with distinct sepals. Example: Brassica, Annona.

b. Synsepalous:
The flower with united or fused sepals. Example: Hibiscus.

2. Duration of Floral Parts:

What is the green part of brinjal fruit? Have you seen similar to this in any other fruits?

a. Caducous or Fugacious Calyx:

Calyx that withers or falls off during the early development stage of flower. Example: Papaver.

b. Deciduous:

Calyx that falls soon after the opening of flower (anthesis) Example: Nelumbo.

c. Persistant:

Calyx that persists and continues to be along with the fruit and forms a cup at the base of the fruit. Example: Brinjal.

d. Accrescent:

Calyx that is persistent, grows along with the fruit and encloses the fruit either completely or partially. Example: Physalis.

3. Shapes of Calyx

Have you noticed the shoe flower’s calyx? It is bell shaped called Campanulate. The fruiting calyx is urn shaped in Withania and it is called urceolate. In Datura calyx is tube like and it is known as tubular. Two lipped calyx is present in Ocimum. Sometimes calyx is coloured and called petaloid. Example: Saraca and Mussanda. In Tridax, calyx is modified into hair like structures are called pappus.

Corolla

Corolla is the most attractive part in majority of the flowers and is usually brightly coloured. Corolla helps to display the flower and attracts the pollinators.

1. Fusion:

a. Apopetalous (Polypetalous):

Petals are distinct. Example: Hibiscus.

b. Sympetalous (Gamopetalous):

Petals are fused. Example: Datura.

Perianth

Can you recall the term homochlamydeous? Undifferentiated calyx and corolla in a flower is called perianth. Each member is called tepal. If the tepals are distinct they are called Apotepalous (Polyphyllous). Example: Allium sativum. Fused tepals are called Syntepalous. (Gamophyllous). Example: Allium cepa.

Aestivation:

Arrangement of sepals and petals in the flower bud is said to be aestivation.

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Flower – Definition of Flower and its Various Types

In a plant, which part would you like the most? Of course, it is a flower, because of its colour and fragrance. The flower is a significant diagnostic feature of angiosperms. It is a modified condensed reproductive shoot. The growth of the flower shoot is determinate.

Whorls of Flower

There are two whorls, accessory and essential. Accessory whorl consists of calyx and corolla and essential whorl comprises of androecium and gynoecium. Flower is said to be Complete when it contains all four whorls. An Incomplete flower is devoid of one or more whorls.

Flower Sex
Flower sex refers to the presence or absence of androecium and gynoecium within a flower.

1. Perfect or Bisexual:
If a flower contains both androecium and gynoecium it is called as a perfect flower.

2. Imperfect or Unisexual:
When the flower contains only one of the essential whorls is called Imperfect flower. It is of two types:

(i) Staminate Flowers:
Flowers with androecium alone.

(ii) Pistillate Flowers:
Flowers with gynoecium alone.

Plant Sex

Plant sex refers to the presence and distribution of flowers with different sexes in an individual plant.

1. Hermaphroditic:
All the flwers of the plant are bisexual.

2. Monoecious:
Both male and female flowers are present in the same plant Example: Coconut.

3. Dioecious:
Male and Female flowers are present on separate plants. Example: Papaya, Palmyra.

4. Polygamous:
The condition in which bisexual and unisexual (staminate/pistillate) flowers occur in a same plant is called polygamous. Example: Musa, Mangifera.

Flower Symmetry

What is the radius of a circle? Cut a paper into round shape, fold it so as to get two equal halves. In how many planes will you get equal halves? In how many planes you can divide a cucumber in two equal halves? A flower is symmetrical when it is divided into equal halves in any plane running through the center. Flower symmetry is an important structural adaptation related to pollination systems.

1. Actinomorphic (or) Radial or Polysymmetric:
The flower shows two mirror images when cut in any plane or radius through the centre. Normally there are more than two planes of symmetry. Example: Hibiscus, Datura.

2. Zygomorphic (Bilateral Symmetry) or Monosymmetric:
The flower can be divided into 2 equal halves in only one plane. Zygomorphic flower can efficiently transfer pollen grains to visiting pollinators. Example: Pisum, Bean.

3. Asymmetric (Amorphic):
Flower lacks any plane of symmetry and cannot be divided into equal halves in any plane. Parts of such flowers are twisted. Example: Canna indica.

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Inflorescene Types and its Characteristics

Have you seen a bouquet being used during functions? Group of flowers arranged together on our preference is a bouquet. But an inflorescence is a group of flowers arising from a branched or unbranched axis with a definite pattern.

Function of inflorescence is to display the flowers for effective pollination and facilitate seed dispersal. The grouping of flowers in one place gives a better attraction to the visiting pollinators and maximize the energy of the plant.

Types of Inflorescence

Based On Position

Have you ever noticed the inflorescence arising from different positions? Where is the inflorescence present in a plant? Apex or axil? Based on position of inflorescences, it may be classified into three major types. They are,

Terminal:
Inflorescence grows as a part of the terminal shoot. Example: Raceme of Nerium oleander.

Axillary:
Inflorescence presents in the axile of the nearest vegetative leaf. Example: Hibiscus rosa-sinensis

Cauliflorous:
Inflorescence developed directly from a woody trunk. Example: Theobroma cocoa, Couraupita guinensis. Observe the inflorescence of Jackfruit and Canon ball tree. Where does it arise?

Based on Branching Pattern and Other Characters

Inflorescence may also be classified based on branching, number and arrangement of flowers, and some specialized structures.

I. Indeterminate (Racemose)
II. Determinate (Cymose)

III. Mixed Inflorescence:
Inflorescence of some plants show a combination of indeterminate and determinate pattern.

IV. Special Inflorescence:
Inflorescence which do not confine to these patterns

I. Racemose

The central axis of the inflorescence (peduncle) possesses terminal bud which is capable of growing continuously and produce lateral flowers is called Racemose inflorescence. Old flowers are at the base and younger flowers and buds are towards the apex. It is further divided into 3 types based on growth pattern of main axis.

1. Main Axis Elongated

The axis of inflorescence is elongated and contains pedicellate or sessile flowers on it. The following types are discussed under main axis elongated type.

a. Simple Raceme:
The inflorescence with an unbranched main axis bears pedicellate flowers in acropetal succession. Example: Crotalaria retusa, Mustard.

b. Spike:
Spike is an unbranched indeterminate inflorescence with sessile flowers. Example: Achyranthes.

c. Spikelet:
Literally it is a small spike. The Inflorescence is with branched central axis. Each branch is a spikelet. Sessile flowers are formed in acropetal succession on the axis.

A pair of inflorescence bracts called glumes is present at the base. Each sessile flower has a lemma (bract) and a palea (bracteole). Tepals reduced to colourless scaly leaves (lodicule). Each flower has stamen and pistil only. Example: Paddy, Wheat.

d. Catkin:
Pendulous spikes with a long and drooping axis bearing small unisexual or bisexual flowers. It is also called ament. Example: Acalypha hispida, Prosopis juliflora.

e. Spadix:
An inflorescence with a fleshy or thickened central axis that possesses many unisexual sessile flowers in acropetal succession. Usually female flowers are found towards the base and male flowers are found at the apex. Entire inflorescence is covered by a brightly coloured or hard bract called a spathe. Example: Amorphophallus, Colocasia.

f. Panicle:
A branched raceme is called panicle. Example: Mangifera, neem. It is also called Compound raceme or Raceme of Racemes.

2. Main axis shortened:

Inflorescence with reduced growth of central axis. There are two types, namely corymb and umbel.

a. Corymb:
An inflorescence with shorter pedicellate flowers at the top and longer pedicellate flowers at the bottom. All flowers appear at the same level to form convex or flat topped racemose inflorescence. Example: Caesalpinia. Compound corymb: A branched corymb is called Compound corymb. Example: Cauliflower.

b. Umbel:
An inflorescence with indeterminate central axis and pedicellate flowers arise from a common point of peduncle at the apex. Example: Allium cepa.

Compound Umbel:
It is a branched umbel. Each smaller unit is called umbellule. Example: Daucas carota, Coriandrum sativum.

3. Main Axis Flattened:
The main axis of inflorescence is mostly flattened (convex or concav) or globose. A head or capitulum is determinate or indeterminate, group of sessile or sub sessile flowers arising on a receptacle, often subtended by an involucre.

a. Head:
A head is a characteristic inflorescence of Asteraceae and is also found in some members of Rubiaceae and Mimosaceae. Torus contains two types of florets:

• Disc floret or tubular floret
• Ray floret or ligulate floret. Based on the type of florets present, the heads are classified into two types.

(i) Homogamous Head:
This type of inflorescence exhibits single kind of florets. Inflorescence has disc florets alone. Example: Vernonia, Ray florets alone. Example: Launaea.

(ii) Heterogamous Head:
The inflorescence possesses both types of florets. Example: Helianthus, Tridax.

Disc florets at the centre of the head are tubular and bisexual, whereas the ray florets found at the margin of the head which are ligulate and pistilate (unisexual).

II. Cymose Inflorescence

Central axis stops growing and ends in a flower, further growth is by means of axillary buds. Old flowers present at apex and young flowers at base.

1. Simple Cyme (Solitary):
Determinate inflorescence consists of a single flower. It may be terminal or axillary. Example: terminal in Trillium grandiflrum and axillary in Hibiscus.

2. Monochasial Cyme (Uniparous):
The main axis ends with a flower. From two lateral bracts, only one branch grows further. It may be Helicoid or Scorpioid.

a. Helicoid:
Axis develops on only one side and forms a coil structure atleast at the earlier development stage. Example: Hamelia, potato.

b. Scorpioid:
Axis develops on alternate sides and often becomes a coiled structure. Example: Heliotropium.

3. Simple Dichasium (Biparous):
A central axis ends in a terminal flower; further growth is produced by two lateral buds. Each cymose unit consists of three flowers of which central one is old one. Ths is true cyme. Example: Jasminum.

4. Compound Dichasium:
It has many flowers. A terminal old flower develops lateral simple dichasial cymes on both sides. Each compound dichasium consists of seven flowers. Example: Clerodendron. A small, simple dichasium is called cymule

5. Polychasial Cyme (Multiparous):
The central axis ends with a flower. The lateral axis branches repeatedly. Example: Nerium

III. Mixed Inflorescence

Inflorescences in which both racemose and cymose patterns of development occur in a mixed manner. It is of the following two types.

1. Thyrsus:
It is a ‘Raceme of cymes’. Indefinite central axis bears lateral pedicellate cymes, (simple or compound dichasia). Example: Ocimum.

2. Verticillaster:
Main axis bears two opposite lateral sessile cymes at the axil of the node, each of it produces monochasial scorpioid lateral branches so that flowers.

IV. Special Inflorescence

The inflorescence that do not show any of the development pattern types are classified under special type of inflorescence.

1. Cyathium:
Cyathium inflorescence consists of small unisexual flowers enclosed by a common involucre which mimics a single flower. Male flowers are organised in a scorpioid manner. Female flower is solitary and centrally located on a long pedicel.

Male flower is represented only by stamens and female flower is represented only by a pistil. Cyathium may be actinomorphic (Example: Euphorbia) or zygomorphic (Example: Pedilanthus). Nectar is present in involucre.

2. Hypanthodium:
Receptacle is a hollow, globose structure consisting of unisexual flowers present on the inner wall of the receptacle. Receptacle is closed leaving a small opening called ostiole which is covered by a series of bracts. Male flowers are present nearer to the ostiole, female and neutral flowers are found in a mixed manner from middle below. Example: Ficus sp. (Banyan, Fig and Pipal).

3. Coenanthium:
Circular disc like fishy open receptacle that bears pistillate flowers at the center and staminate flowers at the periphery. Example: Dorstenia.

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Leaf Definition – Characteristics and Various Types of Functions

Leaves are green, thin flattened lateral outgrowths of the stem. Leaves are the primary photosynthetic organs and the main site of transpiration. All the leaves of a plant together are referred to as phyllome.

I. Characteristics of Leaf

• Leaf is a lateral appendage of the stem.
• It is borne at the node of the stem.
• It is exogenous in origin.
• It has limited growth.
• It does not posses apical bud.
• It has three main parts namely, leaf base, petiole and lamina.
• Lamina of the leaf is traversed by vascular strands, called veins.

II. Functions of the Leaf

Primary Functions

• Photosynthesis
• Transpiration
• Gaseous exchange
• Protection of buds
• Conduction of water and dissolved solutes.

Secondary Functions

1. Storage:
Example: Aloe, Agave.

2. Protection:
Example: Opuntia, Argemone mexicana.

3. Support:
Example: Gloriosa, Nepenthes.

4. Reproduction:
Example: Bryophyllum, Begonia, Zamia.

Parts of the Leaf

Three main parts of a typical leaf are:

1. Leaf base (Hypopodium)
2. Petiole (Mesopodium)
3. Lamina (Epipodium)

I. Leaf Base (Hypopodium)

The part of the leaf attached to the node of the stem is called leaf base. Usually it protects the growing buds at its axil.

Pulvinus:
In legumes leaf base become broad and swollen which is known as pulvinus. Example: Clitoria, Lablab, Cassia, Butea.

Sheathing Leafbase:
In many monocot families such as Arecaceae, Musaceae, Zingiberaceae and Poaceae the leafbase extends into a sheath and clasps part or whole of the internode. Such leafbase also leave permanent scars on the stem when they fall.

II. Petiole (Stipe or Mesopodium)

It is the bridge between lamina and stem. Petiole or leaf stalk is a cylindrical or sub cylindrical or flattened structure of a leaf which joins the lamina with the stem. A leaf with petiole are said to be petiolate. Example: Ficus, Hibiscus. Leaves that do not possess petiole is said to be sessile. Example: Calotropis.

III. Lamina (Leaf Blade)

The expanded flat green portion of the leaf is the blade or lamina. It is the seat of photosynthesis, gaseous exchange, transpiration and most of the metabolic reactions of the plant. The lamina is traversed by the midrib from which arise numerous lateral veins and thin veinlets. The lamina shows great variations in its shape, margin, surface, texture, colour, venation and incision.

Stipules

In most of the dicotyledonous plants, the leaf base bears one or two lateral appendages called the stipules. Leaves with stipules are called stipulate. The leaves without stipules are called exstipulate or estipulate. The stipules are commonly found in dicotyledons. In some grasses (Monocots) an additional out growth is present between leaf base and lamina. It is called Ligule.

Sometimes, small stipule like outgrowths are found at the base of leaflets of a compound leaf. They are called stipels. The main function of the stipule is to protect the leaf in the bud condition.

Venation

The arrangement of veins and veinlets on the leaf blade or lamina is called venation. Internally, the vein contains vascular tissues. Conventionally venation is classified into two types namely, Reticulate venation and Parallel venation.

I. Reticulate Venation

In this type of venation leaf contain a prominent midrib from which several secondary veins arise that branch and anastomose like a network. This type of venation is common in all dicot leaves. It is of two types.

1. Pinnately Reticulate Venation (Unicostate):
In this type of venation there is only one midrib in the centre which forms many lateral branches to form a network. Example: Mangifera indica.

2. Palmately Reticulate Venation (Multicostate):
In this type of venation there are two or more principal veins arising from a single point and they proceed outwards or upwards. The two types of palmate reticulate venation are

(i) Divergent Type:
When all principal veins originate from the base and diverge from one another towards the margin of the leaf as in Carica papaya.

(ii) Convergent:
When the veins converge to the apex of the leaf, as in Indian plum (Zizyphus), bay leaf (Cinnamomum).

II. Parallel Venation

Veins run parallel and do not form a prominent reticulum. It is a characteristic feature of monocot leaves. It is classified into two sub types.

1. Pinnately Parallel Venation (Unicostate)
When there is a prominent midrib in the center, from which arise many veins perpendicularly and run parallel to each other. Example: Musa, Zinger.

2. Palmate Parallel Venation (Multicostate)
In this type several veins arise from the tip of the petiole and they all run parallel to each other and unite at the apex. It is of two sub types.

(i) Divergent Type:
All principal veins originate from the base and diverge towards the margin, the margin of the leaf as in fan palm (Borassus flabelliformis)

(ii) Convergent Type:
All principal veins run parallel to each other from the base of the lamina and join at the apex as in Bamboos, rice, water hyacinth.

Phyllotaxy

The mode of arrangement of leaves on the stem is known as phyllotaxy (Gk. Phyllon = leaf; taxis = arrangement). Phyllotaxy is to avoid over crowding of leaves and expose the leaves maximum to the sunlight for photosynthesis. The four main types of phyllotaxy are:-

1. Alternate
2. Opposite
3. Ternate
4. Whorled.

1. Alternate Phyllotaxy

In this type there is only one leaf per node and the leaves on the successive nodes are arranged alternate to each other. Spiral arrangement
of leaves show vertical rows are called orthostichies. They are of two types.

(a) Alternate spiral:
In which the leaves are arranged alternatively in a spiral manner. Example: Hibiscus, Ficus.

(b) Alternate Distichous or Bifarious:
In which the leaves are organized alternatively in two rows on either side of the stem. Example: Monoon longifolium (Polyalthia longifolia).

2. Opposite Phyllotaxy

In this type each node possess two leaves opposite to each other. They are organized in two different types.

(i) Opposite Superposed:
The pair of leaves arranged in succession are in the same direction, that is two opposite leaves at a node lie exactly above those
at the lower node. Example: Psidium (Guava), Quisqualis (Rangoon creeper).

(ii) Opposite Decussate:
In this type of phyllotaxy one pair of leaves is placed at right angles to the next upper or lower pair of leaves. Example: Calotropis, Ocimum.

3. Ternate Phyllotaxy

In this type there are three leaves attached at each node. Example: Nerium

4. Whorled (Verticillate)

Type of phyllotaxy. In this type more than three leaves are present in a whorl at each node forming a circle or whorl. Example: Allamanda.

Leaf Mosaic

In leaf mosaic leaves tend to fit in with one another and adjust themselves in such a way that they may secure the maximum amount of sunlight with minimum amount of overlapping. The lower leaves have longer petioles and successive upper leaves possess shorter petioles. Example: Acalypha.

Leaf Type

The pattern of division of a leaf into discrete components or segments is termed leaf type. Based on the number of segments

I. Simple Leaf

A leaf is said to be simple when the petiole bears a single lamina; lamina may be entire (undivided) Example: Mango or incised to any depth but not upto the midrib or petiole. Example: Cucurbita.

II. Compound Leaf

Compound leaf is one in which the main rachis bears more than one lamina surface, called leaflets. Compound leaves have evolved to increase total lamina surface. There is one axillary bud in the axil of the whole compound leaf. The leaflets however, do not possess axillary buds.

1. Pinnately Compound Leaf

A pinnately compound leaf is defined as one in which the rachis, bears laterally a number of leaflets, arranged alternately or in an opposite manner, as in Tamarindus, Cassia.

(i) Unipinnate:
The rachis is simple and unbranched which bears leaflets directly on its sides in alternate or opposite manner. Example: Rose, Neem. Unipinnate leaves are of two types.

• When the leaflets are even in number, the leaf is said to be paripinnate. Example: Tamarindus.
• When the leaflets are odd in number, the leaf is said to be imparipinnate. Example: Azadirachta (Neem).

(ii) Bipinnate:
The primary rachis produces secondary rachii which bear the leaflets. The secondary rachii are known aspinnae. Number of pinnae varies depending on the species. Example: Delonix.

(iii) Tripinnate:
When the rachis branches thrice the leaf is called tripinnate. (i.e) the secondary rachii produce the tertiary rachii which bear the leaflets. Example: Moringa.

(iv) Decompound:
When the rachis of leaf is branched several times it is called decompound. Example: Daucus carota, Coriandrum sativum.

2. Palmately Compound Leaf

A palmately compound leaf is defined as one in which the petiole bears terminally, one or more leaflets which seem to be radiating from a common point like fingers from the palm.

(i) Unifoliolate:
When a single leaflet is articulated to the petiole is said to be unifoliolate. Example: Citrus.

(ii) Bifoliolate:
When there are two leaflets articulated to the petiole it is said to be bifoliolate. Example: Zornia diphylla

(iii) Trifoliolate:
There are three leaflets articulated to the petiole it is said to be trifoliolate. Example: wood apple (Aegle marmelos), Clover (Trifolium).

(iv) Quadrifoliolate:
There are four leaflets articulated to the petiole it is said to be quadrifoliolate. Example: Paris quadrifolia, Marsilia

(v) Multifoliolate or Digitate:
Five or more leaflets are joined and spread like fingers from the palm, as in Cleome pentaphylla, Bombax ceiba.

Modifiation of Leaf
The main function of the leaf is food preparation by photosynthesis. Leaves modified to perform some specialized functions. They are described below.

I. Leaf Tendrils

In some plants stem is very weak and hence they have some special organs for attachment to the support. So some leaves are partially or wholly modified into tendril. Tendril is a slender wiry coiled structure which helps in climbing the support. Some of the modification of leaf tendrils are given below:

Entire leaf:
Lathyrus

Stipules:
Smilax

Terminal Leaflet:
Naravelia

Leaf Tip:
Gloriosa

Apical Leaflet:
Pisum

Petiole:
Clematis.

II. Leaf Hooks

In some plants, leaves are modified into hook-like structures and help the plant to climb. In cat,s nail (Bignonia unguis-cati) an elegant climber, the terminal leaflets become modified into three, very sharp, stiff and curved hooks, very much like the nails of a cat. These hooks cling to the bark of a tree and act as organs of support for climbing. The leaf spines of Asparagus also act as hooks.

III. Leaf Spines and Prickles

Leaves of certain plants develop spinesent structures. Either on the surface or on the margins as an adaptation to herbivory and xeric conditions. Example: Zyzypus Argemone mexicana (Prickly poppy), Solanum trilobatum. In xerophytes such as Opuntia (Prickly pear) and Euphorbia leaves and stipules are modified into spines.

Prickles are small, sharp structure which are the outgrowths from epidermal cells of stem or leaf. It helps the plant in scrambling over other plants. It is also protective against herbivory. Example: Rosa spp.

IV. Storage Leaves

Some plants of saline and xerophytic habitats and members of the family Crassulaceae commonly have fleshy or swollen leaves. These succulent leaves store water, mucilage or food material. Such storage leaves resist desiccation. Example: Aloe, Agave, Bryophyllum.

V. Phyllode

Phyllodes are flat, green-coloured leaflike modifications of petioles or rachis. The leaflets or lamina of the leaf are highly reduced or caducous. The phyllodes perform photosynthesis and other functions of leaf. Example: Acacia auriculiformis (Australian Acacia), Parkinsonia.

VI. Pitcher

The leaf becomes modified into a pitcher in Nepenthes and Sarracenia. In Nepenthes the basal part of the leaf is laminar and the midrib continues as a coiled tendrillar structure. The apical part of the leaf is modified into a pitcher the mouth of the pitcher is closed by a lid which is the modification of leaf apex.

VII. Bladder

In bladderwort (Utricularia), a rootless freefloating or slightly submerged plant common in many water bodies, the leaf is very much segmented. Some of these segments are modified to form bladder-like structures, with a trap-door entrance that traps aquatic animalcules.

VIII. Floral Leaves

Floral parts such as sepals, petals, stamens and carpels are modified leaves. Sepals and petals are leafy. They are protective in function and considered non-essential reproductive parts. Petals are usually coloured which attract the insects for pollination. Stamens are considered pollen bearing microsporophylls and carpels are ovule bearing megasporophylls.

Leaf Duration
Leaves may stay and function for few days to many years, largely determined by the adaptations to climatic conditions.

Caducuous (Fagacious)
Falling off soon after formation. Example: Opuntia, Cissus quadrangularis.

Deciduous
Falling at the end of growing season so that the plant (tree or shrub) is leafless in winter/summer season. Example: Maple, Plumeria, Launea, Erythrina.

Evergreen
Leaves persist throughout the year, falling regularly so that tree is never leafless. Example: Mimusops, Calophyllum.

Marcescent
Leaves not falling but withering on the plant as in several members of Fagaceae.