Classification, Identification and Chemical constituents of medicinal plants Presented by, Mahesh Kadagi Sr.MVSc TO, Dr.Shridhar.N.B Asst.professor
Nov 21, 2014
Classification, Identification and Chemical constituents of medicinal plants
Presented by, Mahesh Kadagi Sr.MVSc
TO,
Dr.Shridhar.N.B Asst.professor
Dept of Pharmacology and Toxicology
CLASSIFICATION OF PLANTS Early man classified plants before he had a written
language. Certainly he ate plants, or parts of them, used them for
shelter, and from them prepared weapons for slaughter and defense.
Man talked about these plants. Names for them were a prerequisite to communication and since many kinds of plants were involved, he must have classified them as well as identified and named them
Botanical Taxonomy
The word taxonomy itself comes from the Greek taxo, to put in order, or arrange.
These scientific names hold considerable power, as well as being a universal language with which to communicate about particular plants among different cultures
The scientific or botanical name of a plant is the means by which we give it its unique place in the scientific and biological world.
Plant classification is the placing of known plants into groups or categories to show some relationship.
Scientific classification follows a system of rules that standardizes the results, and groups successive categories into a hierarchy
Plant taxonomy has two aims:
1. To identify all the kinds of plants;
2. To arrange the kinds of plants into a scheme of classification that will show their true relationships
History The first attempt to classify all the plants known was about
300 BC by Theophrastus, the great student of Aristotle.
He classified plants by their habitat or form--the trees were grouped together, the shrubs, the undershrubs, herbs, and so forth.
He also recognized more specific botanical characteristics such as ovary position.
His work, History of Plants, is the oldest botanical work in existence.
The system of Theophrastus was refined only a little by other Greek botanists and herbalists
Dioscorides (first century A.D.) was a military physician under Emperor Nero of Rome.
The Codex of herbal, prepared in 512 A.D from his work was still used until the 16th century
Carolus Linnaeus
Carolus Linnaeus is probably the
single most dominant figure
in systematic classification.
People sent him plants from
all over the world, and he would
devise a way to relate them.
At the age of thirty-two he was the author of fourteen botanical works.
He introduced the binomial system of classification
He classified every plant known to him, and for the first timel gave each plant a binomial
THE BINOMIAL SYSTEM OF CLASSIFICATION
This system is binomial (has two parts), consisting of genus and species, both of which are expressed in Latin.
This binomial system was a vast improvement over same of the old descriptive names for plants used formerly.
Coffea arabica
The genus or generic name is a noun which usually names some aspect of a plant, such as Coffea, the Latinized form of the Arabic word for beverage, kahwah. The species or specific name is usually an adjective that describes the genus. In the case of coffee, the species is arabica, indicating that the plant was thought to originate in Arabia. The coffee plant botanical name, Coffea arabica, refers
to only one plant and cannot be confused with any other. Its botanical name is unique to that particular plant the world over.
Linneaus's book Species Plantarum (The Species of
Plants), published in 1753, continues to influence the naming of plants today.
It is the starting point for checking whether a name has been used previously to insure that each plant is given a unique name.
The earliest name for a plant is usually the official name should a dispute arise.
WHAT THE NAMES MEAN
The genus and species names often tell something about the plant.
They can describe the appearance of the plant, reflect the common name of the plant, indicate a chemical present in the plant, tell how the plant tastes or smells, or describe how the plant grows.
The genus or species name can honor someone, a botanist, a person in power, someone historically prominent.
The name can reflect the country or origin of a plant.
For example, Erythroxylum coca,
the plant from which we derive
cocaine, is named after erythro
meaning red and xylo meaning
wood, literally "red stem." (Coca,
the species name, is the common name
of the plant.)
The jaborandi tree Pilocarpus jaborandi has a genus name which indicates that the alkaloid pilocarpine can be extracted from the plant.
The species name jaborandi means "one who makes saliva or one who spits," referring to the use of the plant as an expectorant
Plant classification is very difficult. Plant species can resemble one another quite closely; plants can sometimes interbreed within species or across species, producing hybrids and varieties that complicate classification.
A case in point is the cinchona tree, a plant instrumental in world history as a result of its alkaloid derivative, quinine, which helped to reduce the incidence of the terrible disease malaria.
The cinchona tree, with its many species and hybrids and varieties within species, has resisted absolute classification.
It's ambivalent ways have left botanists puzzled as to the exact number of species which exist.
In fact, one species grouping of cinchona has been labeled 'Cinchona officinalis.‘
Officinalis (meaning 'of the workshop') is a common species name used for many medicinal plants, particularly, it seems, under the trying circumstances of difficult taxonomy
HOW ARE PLANTS CLASSIFIED?
Science classifies living things in an orderly system through which they can be readily identified.
Living things are grouped into categories of increasing size, based upon relationships within those categories.
Plant Kingdom Ranking would look like this:
Taxonomic ranks- Kingdom: Plantae Division: Class Order: Family: Genera :
CLASS
Angiospermae (Angiosperms)
Plants which produce flowers
Gymnospermae (Gymnosperms)
Plants which don't produce flowers
SUBCLASS
Dicotyledonae (Dicotyledons, Dicots)
Plants with two seed leaves
Monocotyledonae (Monocotyledons,
Monocots)Plants with one seed leaf
ORDER Each class is further divided into several Orders. The names of the Orders end in -ales
FAMILY Each Order is divided into Families. These are plants with many botanical features in common, and is the highest classification
normally used. At this level, the similarity between plants is often easily recognizable by the layman The names of the
Families end in -aceae
SUBFAMILYThe Family may be further divided into a number of sub-
families, which group together plants within the Family that have some significant botanical differences. The names of the
Subfamilies end in -oideae
TRIBE
A further division of plants within a Family, based on smaller botanical differences, but still usually comprising many different
plants. The names of the Tribes end in -eae
SUBTRIBE
A further division, based on even smaller botanical differences, often only recognizable to botanists. The names of the
Subtribes end in -inae
GENUSThis is the part of the plant name that is most familiar. The plants in a Genus are often easily recognizable as
belonging to the same group.
SPECIES This is the level that defines an individual plant. Often, the name will describe some aspect of the plant - the colour of the flowers, size or shape of the leaves, or it may be named after
the place where it was found. Together, the Genus and species name refer to only one plant, and they are used to identify that
particular plantThe name of the species should be written after the Genus
name, in small letters, with no capital letterVARIETY A Variety is a plant that is only slightly different from the
species plant, but the differences are not so insignificant as the differences in a form. Usually abbreviated to var. The name
follows the Genus and species nameFORM A form is a plant within a species that has minor botanical
differences, such as the colour of flower or shape of the leaves. The name follows the Genus and species name, with form (or f.)
before the individual variety name. CULTIVAR A Cultivar is a cultivated variety, a particular plant that has
arisen either naturally or through deliberate hybridisation, and can be reproduced to produce more of the same plant.
The name follows the Genus and species name
Category Scientific Name Common Name
CLASS Angiospermae Angiosperms
SUBCLASS Dicotyledonae Dicotyledons
SUPERORDER Magnoliidae Magnolia Superorder
ORDER Ranunculares Buttercup Order
FAMILY Ranunculaceae Buttercup Family
SUBFAMILY Ranunculoideae Buttercup Subfamily
TRIBE Ranunculeae Buttercup Tribe
GENUS Ranunculus Buttercup
SPECIES (Ranunculus) flammula Lesser Spearwort
SUBSPECIES (Ranunculus flammula) subsp. flammula Lesser Spearwort
VARIETY (Ranunculus flammula subsp. flammula) var. tenuifolius
Narrow-leaved Lesser Spearwort
IDENTIFICATION OF PLANTS
All known plant species have names. It is often necessary to identify an unknown plant, that is, to determine the species to which it belongs and thus its name.
Identification assumes that the plants have already been classified and named.
When you identify a plant, you are basically asking: "Of all known species, which one most closely resembles this individual ?"
Professionals identify plants by keying.
This is a stepwise process of elimination that uses a series of paired contrasting statements, known as a dichotomous key.
Keying is like a trip down a repeatedly forking road: If at the first fork you turn right, you cannot possibly reach any of the towns that lie along the left fork.
Each successive fork in the road eliminates other towns, until you finally reach your destination.
When keying, the user begins by reading the first pair of statements (called a couplet).
For example, a key may begin by asking the user to decide between "plants woody" and "plants not woody."
If the unknown is woody, all non woody species are immediately eliminated from consideration.
Successive couplets will eliminate further possibilities until only one remains, which is the species to which the unknown must belong.
The advantage of this procedure is that the user must only make one decision at a time, rather than mentally confusing with long lists of features of many possible candidates.
Once the plant has been keyed, it is necessary to confirm the identification.
Most books that include keys also include detailed descriptions; some also include illustrations of all or selected species.
If the specimen that was keyed matches the appropriate description and/or illustration, the identification may be assumed to be correct.
The specimen that was keyed can be compared to previously identified specimens of the species as a further check of the identification
Although plant classifications are based upon information from many disciplines, including genetics, chemistry, and molecular biology, identification almost always relies on readily observed structural features, both vegetative and reproductive.
For this reason, it is essential that specimens for identification be as complete as possible.
Those of small plants should include not only all aboveground portions but also the roots.
For large woody plants, a fully expanded twig of the current season will suffice.
In all cases, specimens must include reproductive structures (i.e., flowers, fruits, seeds).
Features that are not represented in the physical specimen (e.g., height or girth of trees, features of the bark, colors or odors that fade in drying) should be noted at the time of collection.
An excellent bibliography of appropriate keys for plants of all parts of earth is provided by Frodin (1983).
As for personal requirements, the most important is a critical eye, that is, the ability to observe carefully and to correctly interpret what is observed.
This requires some familiarity with both plant structures and the terminology used to describe them.
A comprehensive resource for this topic is Radford's introductory textbook (1986). Above all, as with most skills, there is no substitute for plenty of practice.
CHEMICAL CONSTITUENTS
All plants produce chemical compounds as part of their normal metabolic activities. A plant is a storehouse of hundreds of chemicals of diverse biological activities.
Most of the chemicals present in the plants are harmless and are necessary for the survival of both the plant and animal kingdoms.
These are arbitrarily divided into primary metabolites and Secondary metabolites
Primary metabolites- The pathway of metabolism that are essential to life are known as primary metabolism and compounds (such as glucose, amino acids etc.) which are directly involved in these pathways are referred to as primary metabolites such as sugars and fats, found in all plants
Secondary metabolites-compounds other than the
primary metabolites are also produced by plants through secondary pathways
However, the functions of these secondary metabolites (e.g. alkaloids, glycosides etc.) are not clearly understood and they do not appear to be essentially related to the sustenance of life. These compounds not essential for basic function.
The chemical profile of a single plant may vary over time as it reacts to changing conditions.
It is the secondary metabolites and pigments that can have therapeutic actions in humans and Animals,which can be refined to produce drugs.
The functions of secondary metabolites are varied. For example, some secondary metabolites are toxins
used against predators, and others are pheromones used to attract insects for pollination.
Phytoalexins protect against bacterial and fungal attacks.
Allelochemicals inhibit other plants that are competing for soil and light.
Plants upregulate and downregulate their biochemical paths in response to the local mix of herbivores, pollinators and microorganisms.
The word drug itself comes from the French word Drogue - which means 'dried plant'.
Some examples are inulin from the roots of dahlias, quinine from the cinchona, morphine and codeine from the poppy, and digoxin from the foxglove.
The active ingredient in willow bark, once prescribed by Hippocrates, is salicin, which is converted in the body into salicylic acid.
The discovery of salicylic acid would eventually lead to the development of the acetylated form acetylsalicylic acid, also known as "aspirin".
The word aspirin comes from Latin, genus Spiraea, with an additional "A" at the beginning to acknowledge acetylation, and "in" was added at the end for easier pronunciation.
"Aspirin" was originally a brand name, and is still a protected trademark in some countries.
CHEMICAL CONSTITUENTS
On the basis of their chemical nature, the plant chemicals may be categorised as follows:
A) Alkaloids
B) Phenolics
C) Terpenes
D) Glycosides
E) Proteinaceous compounds
F) Organic acids
G) Resins and resinoids.
Alkaloids Alkaloids contain a ring with nitrogen, insoluble in
water. Many alkaloids have dramatic effects on the central
nervous system. Caffeine is an alkaloid that provides a mild lift but the
alkaloids in datura cause severe intoxication and even death.
Not all, but many of the plant alkaloids produce significant pathophysiological effects on human and animal health.
Some of the important alkaloids present in the plant species have been summarized in Table
Type of alkaloid Examples
Tropane or atropine like Atropa belladona , datura,Hyoscyamus
Pyrrolizidine alkaloids Senecio,Crotolaria,Heliotropium
Pyridine/piperidine alkaloid CONIUM(Hemlock), lobelia(Indian tobacco)
Pyrrolidine-pyridine Nicotiana sp.(Tobacco)
Purine alkaloids Coffea sp.(Coffee) Theobroma sp. (Cocoa)
Quinoline alkaloids Cinchona sp. (Quinine tree)
Isoquinoline alkaloids Papaver somniferum (Opium)
Phenolics
Phenolics contain phenol rings.
The anthocyanins that give grapes their purple color, the isoflavones , the phytoestrogens from soya and the tannins that give tea its astringency are phenolics.
Terpenes Terpenes are substances biosynthesized by plants and
contain the branched 5-carbon skeleton of isoprene. On the basis of number of isoprene units present in the
structure of the molecule, Terpenoids are built up from terpene building blocks.
Each terpene consists of two paired isoprenes. The names monoterpenes, sesquiterpenes, diterpenes and triterpenes are based on the number of isoprene units.
The fragrance of rose and lavender is due to monoterpenes.
The carotenoids produce the reds, yellows and oranges of pumpkin, corn and tomatoes.
Glycosides
Glycosides are ether-like combinations of sugars with other organic structures (non-sugar aglycone or genin).
Glycosides are relatively inactive, but when separated from the sugar moiety, the genin or aglycone becomes more active.
During digestion in animals, separation of aglycone takes place due to hydrolysis of the bond between the sugar and aglycone.
Ex: Cadiac Glycosides- Digoxin from Digitalis Oubain from Strophanthus
Proteinaceous compounds Generally, proteins are harmless and often beneficial
agents. Plant proteins in general and reserve proteins of seeds
in particular are an important source of food. After ingestion, proteins get hydrolysed through
various enzymatic reactions in the gastrointestinal tract and the amino acids are absorbed into the system for protein biosynthesis in the body.
However, there are a number of proteins, peptides or amines which are of toxicological importance
ORGANIC ACIDS
Some of acids accumulated by plants, particularly in their fruits e.g.malic acid,tartaric acid,citric acid, ascorbic acid
Resins and resinoids
Cannabis sativa- tetrahydrocannabinol Hypericum perforatum- hypericin
Examples of plants used as medicine
Few herbal remedies are effectively demonstrated positive effect on humans and animals
But many of the studies cited refer to animal model investigations or in-vitro assays only and therefore cannot provide more than weak supportive evidence.
Aloe vera has traditionally been used for the healing of burns and wounds. A systematic review states that the efficacy of aloe vera in promoting wound healing is unclear, while a later review concludes that the cumulative evidence supports the use of aloe vera for the healing of first to second degree burns
Artichoke (Cynara cardunculus) may reduce production cholesterol levels according to in vitro studies and a small clinical study.
Blackberry (Rubus fruticosus) leaf has drawn the attention of the cosmetology community because it interferes with the metalloproteinases that contribute to skin wrinkling.
Black raspberry (Rubus occidentalis) may have a role in preventing oral cancer
Garlic(Allium sativum) may lower total cholesterol levels
Ginger (Zingiber officinale), administered in 250 mg capsules for four days, effectively decreased nausea and vomiting of pregnancy in a human clinical trial
Honey may reduce cholesterol may be useful in wound healing
Rauvolfia Serpentina, high risk of toxicity if improperly used, used extensively in India for sleeplessness, anxiety, and high blood pressure
Peppermint oil may have benefits for individuals with irritable bowel syndrome
Willow bark (Salix alba) can be used for a variety of anti-inflammatory and antimicrobial purposes due to presence of salicylic acid and tannins.