Download 12th Botany Taxonomy of Angiosperms Class Notes D

12th Botany
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Taxonomy of Angiosperms
Lesson 1:TAXONOMY OF ANGIOSPERMS
Taxonomy is the classification of plants based on lows
The term taxonomy includes two Greek words taxis – arrangement and nomos– laws.
Plant taxonomy is otherwise known as systematic botany.
Classification, identification, description and naming the plants are the bases of plant taxonomy.
The taxonomic knowledge about the plants is based on their form and structure.
This knowledge useful in the fields of medicine, agriculture, forestry, etc
The aim of classification :
1. Arrange plants in an orderly sequence based on similarities.
2. The closely related plants are kept within a group and unrelated plants are kept far apart
3. Establish phylogenetic relationships among the different groups
The earliest classification based on only few characters.
They gave importance to vegetative characters.
The later importance given to floral characters
Types of classification :
 Three types of classification –
 1.Artificial
2.Natural
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Class Notes
3.Phylogenetic.
Artificial system :
Based on only a few superficial characters.
1753, Carolus Linnaeus of Sweden in his book “ Species Plantarum” he described 7,300 species.
His division 24 classes based on number, union, length of stamens.
Also known as sexual system of classification.
The importance of floral characters was felt by Linnaeus and so his classification was more important than others.
Defect :
1. Unrelated plants are brought together in a single group
Closely related plants are placed in widely separated groups.
Eg. Plants belonging to Zingiberaceae of Monocotyledons and that of Anacardiaceae of Dicotyledons had been
placed in one group called Monandria (as these possess only one stamen)
2. No importance was given phylogenetic relationships
Natural system :
Based on their natural affinities.
More number of characters are taken into consideration
It is mainly based direct observation of plants.
This system was proposed by British botanists, George Bentham and Sir Joseph Dalton Hooker.
It helps to determine the relationships between various groups of plants.
It does not bring out evolutionary relationships among differen groups.
Phylogenetic system :
Based on evolutionary sequence & genetic relationships among groups of plants.
It employs as many taxonomic characters as possible
Adolf Engler (1844-1930) and Karl Prantl (1849-1893) of Germany published a phylogenetic system in their
monograph on “Die Naturlichen Pflanzen Familien”.
Floral characters : Single whorl of perianth or no perianth and unisexual flowers pollinated primitive characters
when compared to perianth with two whorls, bisexual flowers pollinated by insects.
According to them, members of Asteraceae of dicotyledons and Orchidaceae of monocotyledons were highly
advanced.
Biosystematics :
 Based on similarities and differences that exist in the morphology of plants.
 Morphological characters alone are not the criteria for distinguishing and classifying plants
D.Purushothaman.M.Sc.,M.Sc.,M.Ed.,M.Phil., ,98420-44373,9444348488
12th Botany
Taxonomy of Angiosperms
Class Notes
 Characteristics and differences from other disciplines of science such as Cytology, Genetics,Physiology,
Ecology, Phytogeography, Phytochemistry, Numerical Taxonomy, Molecular Biology, Breeding systems
and any other available sources for classification.
 Biosystematics it is a ‘taxonomy of living populations’.
 Species : basic unit and local breeding population.
 Number of disciplines of science provide datas of all the characters of the individual or a species.
 Thus Help to understand interrelationship, classification and evolution.
 Variations : Due to Genetic,Ecological, Physiological, population dynamic study etc....
 Biosystematist come with solutions for the problem that may arise during their phylogenetic
classification based on their evolution of species under study.
Aims of biosystematics :
 Camp and Gily 1943, coined the term ‘Biosystematics’.
Aims are :
 To delimit the naturally occurring biotic community of plant species.
 To recognise the various groups as separate biosystematic categories such as Ecotypes, Ecospecies,
Cenospecies and Comparium.
 Methods in the study of biosystematics :(3 methods)
 It involves thorough sampling analysis of the taxonomic species vunder study.
 It includes ability of different populations to interbreed among one another
 This will reveal the presence or absence of breeding barriers
 It involves the study of similarity of chromosomes in the hybrids during meiosis.
 Ecotype :
Basic unit in biosystematics, adapted to a particular environment but capable of producing fertile
hybrids with other ecotypes.
o This is equivalent to subspecies of classical taxonomy.
 Ecospecies:
Group of plants comprising one or more ecotypes within the cenospecies, members are able to
interchange their genes.
o Ecospecies is equivalent to species of classical taxonomy.
 Cenospecies :
Group of plants representing one or more ecospecies of common evolutionary origin.
o It is equivalent to subgenus of classical taxonomy.
o Cenospecies are separated by genetic barriers and all hybrids between them are sterile.
 Comparium :
one or more cenospecies that are not able to intercross.
o Complete genetic barriers exist between different comparia.
o biosystematic plays a vital role in separating and solving some of the problems in the
identification
o Biosystematist provides all the necessary data in solving the real position of species
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Binomial nomenclature
It is Naming the plants on a scientific basis
Naming of the plants is useful in assigning their identity and relationship.
In 18 century,the names were polynomials (several words in series constituting more description )
Eg. Caryophyllum saxatilis folis gramineus umbellatis corymbis (meaning: Caryophyllum growing on rocks,
having grass like leaves with umbellate corymbose inflorescence )
Lengthy names are difficult to remember and use,
Carolus Linnaeus suggested a system of binomial nomenclature.
This was introduced by Gaspard Bauhin (1623) but properly used by Linnaeus in his book Species
Plantarum.
In this every species is given a name of two words.
Eg.mango tree - Mangifera indica.
Mangifera- genus and indica -species.
D.Purushothaman.M.Sc.,M.Sc.,M.Ed.,M.Phil., ,98420-44373,9444348488
Unit-1: Taxonomy of Angiosperms
Plant
Common Name Inflorcence
Croton sparsiflorus Eli amanakku Simple raceme,
Acalypha indica Kuppaimeni
Catkin.
Phyllanthus amarus, the male and female flowers are axillary and solitary.
Flower
Bracteate, ebracteolate, pedicellate, unisexual, monoecious or dioecious,
Incomplete and hypogynous.
In Euphorbia , the male flower is represented by a single stamen and female flower by a single pistil.
Perianth :
In Croton sparsiflorus, the male flowers have two whorls of perianth and
female flowers have a single whorl of perianth.
The male and female flowers of Euphorbia are usually devoid of perianth i.e aphyllous.
The tepals are polyphyllous in Phyllanthus amarus and gamophyllous in Ricinus communis
Androecium :
Stamen one to many, free or united.
In Ricinus communis, the stamen is polyadelphous and the filaments are branched.
They are fused into several bundles.
Anthers are dithecous.
Rudimentary ovary called pistillode is often present in male flowers.
Gynoecium :
Ovary superior, tricarpellary and syncarpous.
Ovary trilocular with one or two ovules in each locule on axile placentation.
Ovary is distinctly three lobed.
Styles three, each ending in a bifid stigma.
Fruit :
Most commonly schizocarpic capsule or drupe.
It is regma in Ricinus communis, dehiscing into three cocci.
Seed
Endospermous.
MUSACEAE - the banana family
Systematic position
Class
:
Monocotyledonae
Series
:
Epigynae
Family
:
Musaceae
General characters
Distribution
World wide distribution mainly in tropical regions
World : 6 genera and about 150 species.
India : 2 genera and about 25 species.
Habit
Perennial herbs attaining considerable height, perennating by means of rhizome
(eg. Musa paradisiaca - Banana)
Rarely trees (eg. Ravenala madagascariensis - Traveller’s palm)
Watery sap is present.
Root
Fibrous adventitious root system
Stem
In Musa the real stem is underground called rhizome.
The apparent, unbranched, errect and areal pseudostem is formed by the long, stiff and sheathy leaf bases which are rolled around one another to form an aerial pseudostem.
The central axis that is concealed at the bottom of the pseudostem is called shaft.
At the time of flowering, the shaft elongates, pierces through the pseudostem and produces an inflorescence terminally.
Musa is a monocorpic perennial, because it produces flowers and fruits once during its life time.
In Ravenala, the stem is aerial and woody.
Leaf
Simple with a long and strong petiole.
The leaf blade is large and broad with sheathy leaf base.
The leaf is extipulate and obtuse.
The pinnately parellel venation extends upto the leaf margin.
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+2 Botany
The phyllotaxy is spiral in Musa but in
Phyllotaxy in Ravenala is distichous i.e. the leaves are arranged in two rows on the same sides.
Inflorescence
In Musa, the inflorescence is branced spadix.
The flowers are protected by large, brightly coloured, spirally arranged, boat shaped bracts called spathes.
When the flowers open, the spathes roll back and finally fall off.
In Ravenalea, the inflorescence is a compound cyme.
In Musa, the flowers are polygamous
i.e. staminate flowers, pistillate flowers and bisexual flowers are present in the same plant.
The male flowers lie within the upper bracts, the female flowers within the lower bracts and the bisexual flowers within the middle bracts.
Flowers
Brateate, ebractiolate, sessile, trimerous, unisexual or bisexual, when unisexual, the flowers are monoecious.
The flowers are zygomorphic and epigynous.
Perianth
Tepals 6, arranged in two whorls of 3 each, free or united.
In Musa, the three tepals of the outer whorl and the two lateral tepals of the inner whorl are fused by valvate aestivation to form 5 toothed tube like structure.
The inner posterior tepal is alone free.
It is distinctly broad and membranous.
Androecium
Basically stamens 6, in two whorls of 3 each, arranged opposite to the tepals.
In Musa only 5 stamens are fertile and the inner posterior stamen is either absent
or represented by a staminode.
In Ravenala, all the 6 stamens are fertile.
Anthers are dithecous and they dehisce by vertical slits.
The filament is filiform and rudimentary ovary or pistillode is often present in the male flower.
Gynoecium
Ovary inferior, tricarpellary, syncarpous, trilocular, numerous ovules on axile placentation.
The style is simple and filiform.
The stigma is three lobed.
Fruit
An elongated fleshy berry without seeds eg. Musa
A capsule
eg. Ravenala.
Seed:
Non - endospermous
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Bio-Botany