Lecture 02

Structure of The Flower

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Magnoliophyta, also called angiosperms). The stalk of the flower is called the pedicel and is swollen at the tip forming the receptacle.

Types of Flowers Based on Placements of Whorls in Receptacle

Hypogynous: Flowers coming under this type have petals, sepals and stamens arranged at the base of the ovary in a convex receptacle.

Perigynous: The sepals, petals, stamens and ovary lie in the same plane.

Epigynous: The sepals, petals and stamens are placed above the ovary.

The Floral whorls

A.   Calyx

The outermost whorl consisting of units called sepals; these are typically green and enclose the rest of the flower in the bud stage.

Types of Calyx Based on Fusion

Polysepalous: Polysepalous type includes flowers having free sepals or in other words, the sepals are not fused.

Gamosepalous: Flowers belonging to gamosepalous (synsepalous) type have fused or jointed sepals, either wholly or at the base only.

B.   Corolla

The next whorl toward the apex, composed of units called petals, which are typically thin, soft and colored to attract animals that help the process of pollination.

Types of Corolla Based on Fusion

Polypetalous: Flowers having free petals.

Gamopetalous: Flowers belonging to gamopetalous (sympetalous) type have fused or united petals.

Perianth Types Based on Presence or Absence of Parts

Achlamydeous: Without perianth. Chlamydeous: With perianth. Dichlamydeous: With perianth composed of distinct calyx and corolla. Homochlamydeous: With perianth composed of similar parts, each part a tepal.

Aestivation

Refers to the positional arrangement of the parts of a flower within a flower bud before it has opened. It can be an important taxonomic diagnostic. The types of aestivation are:

1. Units meet without overlapping …………………………...…..Valvate

1. Units overlapped…………………………………………..…Imbricate

          2. Units overlapped all in the same direction………..…..Contorted

                                                                                         (Clockwise or Anticlockwise)

          2. Units overlapped not in the same direction

                   3. Each unit overlapping the one

posterior to it……………………………....Ascending

                   3. Each unit overlapping the one

anterior to it……………………………....Descending

                   3. Two units overlapping with both the edges,

two underlapping with both edges

and one unit over- and under-lapping….. Quincuncial

C.   Androecium (from Greek andros oikia: man's house)

The next whorl, consisting of units called stamens. Stamens consist of two parts: a stalk called a filament, topped by an anther where pollen is produced by meiosis and eventually dispersed.

Androecial Types Based on Fusion of Parts

Apostemonous: With separate stamens. Monadelphous: With one group of stamens connate by their filaments. Diadelphous: With two groups of stamens connate by their filaments. Polydelphous: With several groups of stamens connate by their filaments. Syngenesious: With fused anthers. Petalostemonous: With filaments fused to corolla. Gynostemial: With fused stamens and carpels (stigma and style).

Anther Types Based on Dehiscence

Extrorse: Dehiscing longitudinally outward. Introrse: Dehiscing longitudinally inward. Latrorse: Dehiscing longitudinally and laterally. Terminal: Dehiscing through a pore or slit at apex of theca.

Anther Attachment

Basifixed: Anther attached at its base to apex of filament. Apicifixed: Anther attached at its top to apex of filament. Dorsifixed: Anther attached dorsally and medially to apex of filament. Versatile: Dorsifixed but anther seemingly swinging free on the filament.

D. Gynoecium (from Greek gynaikos oikia: woman's house)

The innermost whorl of a flower, consisting of one or more units called carpels. The carpel or multiple fused carpels form a hollow structure called an ovary, which produces ovules internally, The supportive stalk, the style; becomes the pathway for pollen tubes to grow from pollen grains adhering to the sticky tip the stigma; the receptor of pollen.

Gynoecial Types Based on Fusion

Apocarpous: With carpels separate. Syncarpous: With stigmas, styles, and ovaries completely fused. Synovarious: With ovaries of adjacent carpels completely fused, styles and stigmas separate. Synstylovarious: With ovaries and styles of adjacent carpels completely fused, stigmas separate.

Style Types Based on Insertion

Gynobasic: Attached at base of ovary in central depression. Terminal: attached at the end of the ovary.

Style Types Based on Branching

Simple: one style from one carpel. Single: one style from more than one carpel. Free: branched style.

Stigma Types Based on Shape

Capitate: Head-like. Clavate: Club-shaped. Discoid: Disc-like. Fimbriate: Fringed. Lobed: Divided into lobes. Plumose: Feather-like. Terete: Cylindrical and elongate.

Types of Placentation

The arrangement of ovules within the ovary is known as placentation.

1. Ovary more than one locule, ovules

attached to axile placenta) ………………………………..…..Axile

1. Ovary one locule

          2. One ovule

                   3. Placenta at the base of the ovary………………...…..Basal

                   3. Placenta at the top of the ovary………………...…..Apical

          2. Many ovules

                   4. Placenta on a ridge along the ventral

suture of the ovary……………………….....Marginal

                   4. Ovules on peripheral walls of the ovary……….…Parietal

                   4. Ovules on the central placenta…………...….Free central

Ovule Types Based on Orientation of Ovule Body in Relation to the Funiculus and Micropyle

Orthotropous or Atropous. With straight body so that funicular attachment is at one end and micropyle at other. Anatropous. With body completely inverted so that funiculus is attached basally near adjoining micropyle area. Amphitropous. With body bent or curved on both sides so that the micropyle is near the medially attached funiculus. Campylotropous. With body bent or curved on one side so that micropyle is near medially attached funiculus.

Sex of The Flower

In the majority of species, individual flowers have both functional carpels and stamens. These flowers are described by botanists as being perfect or bisexual. Some flowers lack one or the other reproductive organ and called imperfect or unisexual. If unisexual flowers are found on the same individual plant but in different locations, the species is said to be monoecious. If each type of unisexual flower is found only on separate individuals, the plant is dioecious.

Symmetry of the Flower

Many flowers have a symmetry, if the perianth is bisected through the central axis from any point, symmetrical halves are produced, the flower is called regular or actinomorphic. When flowers are bisected and produce only one line that produces symmetrical halves the flower is said to be irregular or zygomorphic.

Pollination

The deposition of pollen on the stigma of the gynoecium.

Classification of pollination

1. Pollination takes place internally when

the flowers are closed…………………………..……. Cleistogamy

1. Pollination takes place when

the flowers are open…………………………..……. Chasmogamy

2. Deposition of pollen on the stigma of

the same flower…………………………………..Autogamy

                                                                                                              (Self pollination)

3. Pollen deposited directly from the

anthers on to the receptive stigma…………….. Direct

3. Pollen deposited on the stigma

by an external agent…………..................….. Indirect

2. Deposition of pollen on the stigma of

another flower……………………………..………Allogamy

                                                                            (Cross pollination)

4. Pollination by another flower of the                 

same inflorescence on the same plant………………………….…..…… Geitonogamy

4. Pollination by pollen from another

plant………………………………...……. Xenogamy

Types of Pollination Based on Agents of Pollination

A. Anemophyly: Pollination by wind.

B. Hydrophily: Pollination by the agency of water.

C. Zoophily: Pollination by the agency of the animals.

          1. Ornithophily: Pollination by birds.

          2. Chiropteriphily: Pollination by bats.

          3. Melacophily: Pollination by slugs and snails.

          4. Entomophily: Pollination by insects.

Key to Types of Fruits

1. Fruit derived from several flowers ............................MULTIPLE FRUIT

                     “Composite”

                          (Pineapple, Mulberry, Fig)

1. Fruit derived from a single flower

2. Derived from more than one pistil ..............AGGREGATE FRUIT

            (Raspberry, Strawberry)

2. Derived from a single pistil ...................................SIMPLE FRUIT

3. Fruit fleshy, usually indehiscent (not splitting)

4. Flesh of fruit derived from

       a hypanthium that surrounds

the papery carpels ........................................POME

                                                  (Apple, Pear)

4. Flesh of fruit derived from the ovary wall

5. Pericarp with an outer fleshy

layer and an inner bony layer

(the stone) ................................................. DRUPE

                                                                                                                                                             (Peach)

5. Pericarp without an inner bony layer,

more or less fleshy

throughout .......................................BERRY

                                                                                                                                                 (Tomato, Grape)

Modifications of the berry type of fruit may be defined as follows:

6. Septae evident in cross section; the outer      layer leathery.....................HESPERIDIUM

                                                                                                                                                 (Orange, Lemon)

6. Septae lacking; the outer layer leathery to hard and woody...................................PEPO

                         (Cucumber, Watermelon, Cantaloupe)

                           

3. Fruit dry at maturity

7. Fruit indehiscent (not splitting open)

8. With one/more wings .........................SAMARA

                                                                                                                                              (Maple, Ash, Elm)

8. Without wings

9. From a compound pistil

10. Shell becoming hard and bony.............................................NUT

                                                                                                                                     (Oak, Walnut, Hazelnut)

10. Shell not bony….…..CYPSELLA

    (Sunflower)

9. From a simple pistil, shell not bony

11. Pericarp fused to the

seed .............GRAIN (CARYOPSIS)

                         (Wheat, Rice, Corn)

11. Pericarp separable from

the seed ..............................ACHENE

                                                                                                                                 (Sedges, Sunflower, Aster)

7. Fruit dehiscent (splitting open)

12. From a simple pistil (1 carpel)

13. Splitting on two

sutures .........................................LEGUME

                                                                                                                                                          (Pea, Bean, Alfalfa)

13. Splitting on one

suture ........................................FOLLICLE

       (Milkweed, Larkspur)

12. From a compound pistil (carpels 2 or more, united)

14. Carpels separating from each

other but each retaining

its seed.................................SCHIZOCARP

          (Parsnip, Carrot)

14. Carpels splitting, releasing 1 or more seeds

15. Fruit 2-celled, the two valves splitting away from a persistent,

thin partition or septum

(replum)……………...........SILIQUE

      (SILICULE if short)

         (Mustard)

15. Fruit 1-several-celled, the partition not persistent if fruit

2-celled ............................ CAPSULE

        (Willow, Iris, Yucca)

There are modifications of the capsular type of fruit as follows:

16. Opening by a lid

17. With a single

seed ..............UTRICLE

       (Pigweed)

17. With several

seeds .................. PYXIS

           (Portulaca)

16. Opening by holes near the top…………….. PORICIDAL

      (Poppy)

16. Opening by splitting lengthwise

18. Splitting on the septae ….SEPTICIDAL

    (Yucca)

18. Splitting between the septae and in the locules

……....LOCULICIDAL

          (Glacier Lily)

18. Splitting on both septae and locules

……....SEPTIFRAGAL

              (Datura)

INFLORESCENCE or ANTHOTAXY

The flowers may be borne singly or in clusters. Flowers borne singly are solitary, and those in clusters together with the stems and bracts associated with them, form an inflorescence. Inflorescence is the cluster of flowers borne on a common stalk, un-branched or branched, The peduncle is the stalk that supports a flower cluster. It is a branch. The term pedicel is applied to the flower stalk of a single flower.

Key to Types of Inflorescence

1. Racemose

Main axis not arrested or terminated by a flower:- Racemose, Indefinite, Acropetal, Ascending or Centripetal.

1. Simple, with main axis unbranched:-

2. Flowers pedicellate

3. Of somewhat equal length on a

comparatively elongated axis....Raceme

3. The lower ones longer than the

upper and the main axis short...Corymb

3. Of nearly equal length on an

undeveloped main axis…….…Umbel

2. Flowers sessile

4. On a comparatively elongated

main axis……………….…….Spike

4. A pendulous spike….…………….Catkin

                                                          (Ament)

4. A fleshy spike…………….……….Spadix

4. The main axis condensed…………Head

                                                        (Capituum)

1. Compound, with main axis branched once or more

5. Branched racemose……………….Panicle

                                                (Compound Raceme)

5. Corymbs corymbose ……………..Compound Corymb

5. Umbels is an umbel……………....Compound Umbel

5. Spikes spicate…………………....Compound Spike

2. Cymose

Main axis arrested and terminated by a flower:- Cymose, Definite, Basipetal, Decending or Centrifugal.

1. A cyme with only one branch…………………….....Monochasial

2. Branching regularly to one side only………....Helicoid

2. Branching alternately to either side………..…Scorpioid

1. A cyme with two branches……………………..……Dichasial

1. A cyme with more-than two branches……….……...Polychasial

3. Special

1. A pair of opposite cymes seemingly

confluent round the main axis…………………..Verticillaster

1. Flowers unisexual borne on the

inside of an hollowed out axis or

receptacle, opening to the outside

by an opening guarded by incurved hairs………Hypanthodium

1. A cymose inflorescence reduced to look like

a single flower ; flowers unisexual and naked,

with a single female flower in the centre

surrounded by several male flowers, arising

from the bottom of a cup-like involucre……..…Cyathium

A System of classification

1. Perianth absent (naked flower)…………………………..Achlamydeae

1. Perianth present………………………………..………….Chlamydeae

          2. One whorl present…………………….…….Monochlamydeae     

          2. Two whorls present……………..………...…..Diplochlamydeae

                   3. Perianth undifferentiated……………...Homochlamydeae

                   3. Perianth differentiated into

                             clayx and corolla……………..…..Heterochlamydeae

                             4. Petals united, stamens≤ 5,

epipetalous, single style…………...Sympetalae

                             4. Not so…………………..……….Archichlamydeae

Lecture 01

Taxonomy of Flowering Plants

Plant taxonomy is the science that finds, describes, classifies, identifies, and names plants. It thus is one of the main branches of taxonomy.

Plant taxonomy is closely allied to plant systematics, and there is no sharp boundary between the two. In practice, "plant systematics" is involved with relationships between plants and their evolution, especially at the higher levels, whereas "plant taxonomy" deals with the actual handling of plant specimens.

Goals of plant taxonomy

The goals are the identification, nomenclature and classification of plants.

A. Plant identification is the determination of the identity of an unknown plant by comparison with previously collected specimens or with the aid of books or identification manuals.

B. Plant nomenclature is the determination of the correct name of a known plant according to a known system (International Code of Botanical Nomenclature; ICBN).

Vernacular name versus Scientific name

A vernacular name of an organism (a common name) is a name in general use within a community; it is often contrasted with a scientific name. On the other hand the scientific name has Greek or Latin origin. Linnaeus 1753 gave the Binomial Nomenclature (each plant should have two epithets; the first is the generic name written in capital letter and the second is the specific epithet).

C. 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. For example, the family to which the lilies belong is classified as follows:

Kingdom: Plantae, Division: Magnoliophyta, Class: Liliopsida, Order: Liliales, Family: Liliaceae, Genera : ... ...

The classification of plants results in an organized system for the naming and cataloging of future specimens, and ideally reflects scientific ideas about plant inter-relationships.

Systems of Classification

A. Artificial Classifications classifies organisms by means of one or few characters.

B. Natural Classification reflects the situation as it is believed to exist in nature and utilizes all information available at the time such as habit of the plant.

C. Phylogenetic Classification classifies organisms according to their evolutionary sequence.

Determination the degree of primitiveness or evolutionary advancement of a plant group

Bessey's system was based on a series of "dicta" or statements of the guiding principles he used in determining the degree of primitiveness or evolutionary advancement of a plant group. Following are Bessey's dicta:

A. General dicta

1. Evolution is not always upward, but often it involves degradation and degeneration.

2. In general, homogeneous structures (with many and similar parts) are lower, and heterogeneous structures (with fewer and dissimilar parts) are higher.

3. Evolution does not necessarily involve all organs of the plant equally in any particular period, and one organ may be advancing while another is retrograding.

4. Upward development is sometimes through an increase in complexity, and sometimes by a simplification of an organ or a set of organs.

5. Evolution has generally been consistent, and when a particular progression or retrogression has set in, it is persisted in to the end of the phylum.

6. In any phylum the holophytic (chlorophyll-green) plants precede the colorless (hysterophytic) plants, and the latter are derived from the former.

7. Plant relationships are up and down the genetic lines, and must constitute the framework of phylogenetic taxonomy.

B. Dicta related to the general structure of the flowering plants

8. The stem structure with collateral vascular bundles arranged in a cylinder is more primitive than that with scattered bundles and the latter are to be regarded as derived from the former.

9. Woody stems (as of trees) are more primitive than herbaceous stems, and herbs are held to have been derived from trees.

10. The simple, unbranched stem is an earlier type, from which branching stems have been derived.

11. Historically the arrangement of leaves in pairs on the stem is held to have preceded the spiral arrangement in which the leaves are solitary at the nodes.

12- Historically simple leaves preceded branched ("compound") leaves.

13. Historically leaves were first persistent ("evergreen") and later deciduous.

14. The reticulated venation of leaves is the normal structure, and the parallel venation of some leaves is a special modification derived from it.

C. Dicta related to the structure of the flower

15. The polymerous flower structure precedes, and the oligomerous structure follows from it, and this is accompanied by a progressive sterilization of sporophylls.  

16. Petaly is the normal perianth structure, and apetaly is the result of perianth reduction (aphanisis).

17. The apochlamydeous perianth is earlier and the gamochlamydeous perianth is derived from it by symphysis of the members of perianth whorls.                                               

18. Actinomorphy is an earlier .structure than zygomorphy and the latter results from a change from similar to a dissimilar growth of the members of the perianth whorls.

19. Hypogyny is the more primitive structure, and from it epigyny was derived later.

20. Apocarpy is the primitive structure, and from it syncarpy was derived later.

21. Polycarpy is the earlier condition, and oligocarpy was derived from it later.

22. The endospermous seed is primitive and lower, while the seed without endosperm is derived and higher.

23. Consequently, the seed with a small embryo (in endosperm) is more primitive than the seed with a large embryo (in scanty or no endosperm).

24. In earlier (primitive) flowers there are many stamens (polystemonous) while in later flowers there are fewer stamens (oligostemonous).

25. The stamens of primitive flowers are separate (apostemonous), while those of derived flowers are often united (synstemonous).

26. The condition of powdery pollen is more primitive than that with coherent or massed pollen.

27. Flowers with both stamens and carpels (monoclinous) precede those in which these occur on separate flowers (diclinous).

28. In diclinous plants the monoecious condition is the earlier, and the dioecious later.

Trends in plant taxonomy

1. Orthodox Criteria

a-The macro-morphological characters

include the characters of the root system and other underground parts (rhizome, tuber, bulb). The macro-morphological characters of the aerial parts include the characters of stem, leaf, flower, inflorescence, fruit... etc.

b- The micro-morphological characters

The anatomical characters of the vegetative structures have been of

importance in separating higher categories, such as gymnosperms from

angiosperms and monocot from dicot.

2. Palynological criteria

Palynology is the study of pollen grains and spores including pollen morphology such as:

1. Composition of pollen grains

2. Stratification of the pollen wall (sporoderm)

3. Exine sculpture

4. Number, type and position of apertures in sporoderm

5. Shape of pollen.

3. Chemotaxonomy Criteria

Plant Chemotaxonomy is the application of chemical data to systematic problems.

4. Embryology Criteria

The embryological characters of taxonomic value in delimiting plant groups

include the anther; development and organization of the pollen grains; development and structure of the ovule; megasporogenesis and development of the embryosac; fertilization; endosperm; embryo and seed coat.

5. Cytology

The utilization of the characters and phenomena of cytology for the explanation of taxonomic problems is referred as cytotaxonomy.

6. Molecular Systematics

The molecular analyses of the three angiosperm genomes: chloroplast DMA

(cp DMA), mitochondrial DMA (mt DNA) and nuclear DMA (n DNA) are applicable to the study of phylogenetic and taxonomic relationships.

7- Physiological Criteria

Plants show differences in their metabolic process and chemical reaction. On this basis, similarities and differences can be established amongst the plants.