Biology

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International Code of Botanical Nomenclature (ICBN)

Assigning name for a plant is known as Nomenclature. This is based on the rules and recommendations of the International Code of Botanical Nomenclature. ICBN deals with the names of existing (living) and extinct (fossil) organisms. The elementary rule of naming of plants was first proposed by Linnaeus in 1751 in his Philosophia Botanica.

In 1813 a detailed set of rules regarding plant nomenclature was given by A.P. de Candolle in his famous work “Theorie elementaire de la botanique”. Then the present ICBN was evolved by following the same rules of Linnaeus, A.P. de Candolle and his son Alphonse de Candolle.

ICN Principles

International Code of Nomenclature is based on the following six principles.

1. Botanical nomenclature is independent of zoological and bacteriological nomenclature.
2. Application of names of taxonomic group is determined by means of nomenclatural types.
3. Nomenclature of a taxonomic group is based on priority of publication.
4. Each taxonomic group with a particular circumscription, position and rank can bear only one correct name.
5. Scientific names of taxonomic groups are treated as Latin regardless of their derivation.
6. The rules of nomenclature are retroactive unless expressly limited.

Codes of Nomenclature

ICN has formulated a set of rules and recommendations dealing with the botanical name of plants. International Botanical Congress is held at different places every six years. Proposals for nomenclatural changes and changes in rules are discussed and implemented. Changes are published in their website.

18^th International Botanical Congress held in 2011 at Melbourne, Australia made the following major changes.

1. The code now permits electronic publication of names of new taxa.
2. Latin diagnosis or description is not mandatory and permits the use of English or Latin for the publication of a new name (Art-39).
3. “One fungus, one name” and “one fossil one name” are important changes, the concept of anamorph and teleomorph (for fungi) and morphotaxa (for fossils) have been eliminated. (Previously, sexual and asexual stages of the fungus/fossils were provided with different names).
4. As an experiment with “registration of names” new fungal descriptions require the use of an identifier from a “recognized repository”.
5. There are two recognized repositories Index fungorum and Myco Bank.

19^th International Botanical Congress was held in Shenzhen in China in 2017. Changes accepted by International Botanical Congress are yet to be published.

Vernacular Names (Common Names)

Vernacular names are known as common names. They are very often descriptive and poetic references to plants. Common name refer to more than one plant or many plants may have same common name. These names are regional or local and are not universal. Example: Albizia amara. L belongs to Mimosaceae is called as Usilai in South Tamilnadu and Thurinji in North Tamilnadu.

Scientific Names/Botanical Names

Each and every taxon as per the ICN (species, genus, family etc) can have only one correct scientific name. Scientific name of a species is always a binomial. These names are universally applied. Example: Oryza sativa L. is the scientific name of paddy.

Polynomial

Polynomial is a descriptive phrase of a plant. Example: Ranunculus calycibus retroflexis pedunculis falcatis caule erecto folius compositis. It means butter cup with reflexed sepals, curved flower stalks, erect stem and compound leaves. Polynomial system of naming a plant is replaced by a binomial system by Linnaeus.

Binomial

Binomial nomenclature was first introduced by Gaspard Bauhin and it was implemented by Carolus Linnaeus. Scientific name of a species consists of two words and according to binomial nomenclature, the first one is called genus name and second one is specific epithet. Example: Mangifera indica. Mangifera is a genus name and indica is specific epithet. This system is in vogue even now.

Author Citation

This refers to valid name of the taxa accompanied by the author’s name who published the name validly. Example: Solanum nigrum L. There are two types of author citation.

Single Author:

When a single author proposed a valid name, the name of the author alone is accompanied by his abbreviated name. Example: Pithecellobium cinereum Benth.

Multiple Authors:

When two or more authors are associated with a valid publication of name, their names should be noted with the help of Latin word et or &. Example: Delphinium viscosum Hook. f. et Thomson. Standard Form of Author’s Abbreviations has to be followed.

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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

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.