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
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
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
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
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