Study of angiosperm flower

Definition:

 Flower is the specialized reproductive
shoot of an angiosperm plant
 A typical flower consists of four whorls of
modified leaves viz.
Calyx, Corolla, Androecium and
Gynoecium.

Technical terms used in description
of a flower.
 Monoecious : A condition where both
male and female flowers are borne in the
same plant.

 Dioecious: A condition where the male
flowers are borne on male plant and
female flowers on female plant.
Borassus flabellifer (Toddy Palm) Borassus flabellifer (Toddy Palm)
Female Plant Male Plant

 Pistillate flower: Flowers having only
female reproductive organ. (Gynoecium)

Cucurbita Female flower

 Staminate flower: Flowers having only
male reproductive organ. (Androecium)

Cucurbita Male flower

 Actinomorphic: Flowers which are
symmetrical in all direction. i.e. Each whorl
of the flower consisting of same size.

Tribulus flower

 Zygomorphic: Flowers which are
symmetrical in one direction only. i.e.
Each whorl of the flower consisting of
different sizes of petals and sepals.
Cassia flower

 Unisexual flower: flower having only one
functional sex of the reproductive organ.
(either ale or female sex organ)

Castor flower

 Bisexual flower: Flower having both male
and female functional sex organs
(Gynoecium and androecium)

Tribulus flower

 Pedicellate flower: Flowers having a
pedicel /stalk

Hibiscus flower

Sessile flower: Flowers without a
pedicel /stalk

Achyranthes flower

 Bracteate flower: Flowers having a bract
(a small leaf like structure subtending a
flower

Rose Bougainvillea
Ebracteate flower: Flowers without a
bract

Mimosa

 Bracteolate flower: Flowers having
bracteoles (Small leaf like structures on
the flower stalk)

Ebracteolate flower: Flowers without
bracteoles .

 Homochlamydeous flower: Flowers in
which the perianth is not differentiated into
calyx and corolla.

Heterochlamydeous flower: Flowers in
which the perianth is differentiated into
calyx and corolla.

 Complete flower: Flowers having all the
four whorls viz.
Gynoecium.

Incomplete flower: Flowers lacking one
of the four whorls viz.
Gynoecium.

 Epigynous flower: Flowers in which the
floral parts are arising above the level of
the ovary.

Hypogynous flower: Flowers in which
the floral parts are arising below the level
of the ovary.

 Perigynous flower: Flowers in which the
floral parts are arising from the rim of the
hypanthial cup of the ovary.

Parts of a flower
 Out of the four whorls of the flower, Calyx
and Corolla are called accessory whorls as
they do not directly take part in reproduction

 Androecium and Gynoecium are considered
as essential whorls.

Calyx: 1st Whorl of the flower
 It is composed of sepals.
 Polysepalous: The sepals are free from
each other.
ROS
E

 Gamosepalous: The sepals are fused with
each other.
HIBISCU
S

COROLLA: 2nd Whorl of the flower
 It is composed of petals
 Polypetalous: The petals are free from
each other

ROS
E

 Gamopetalous: The petals are fused with
each other

DATURA

Aestivation: The arrangement of
petals & sepals in the flower bud
 Valvate: Here the floral leaves (Petals &
Sepals) are arranged side by side.

Aestivation:
 Twisted: Here the floral leaves show
regular overlapping in one direction.

HIBISCU
S

Aestivation:
 Imbricate (ascendingly imbricate): Here
one floral leaf is completely in (posterior
petal), one completely out (anterior petal)
and remaining are overlapping in one
direction.

Aestivation:
 Quincuncial: It is rare and found in
pentamerous flower only. Here two petals
are innermost, two petals are outermost
and one is alternate

Cassia
occidentalis

Aestivation:
 Vexillary: It is rare and found in pentamerous
flower only. Here two petals are
innermost, two petals are outermost and one
is alternate. Here the posterior petal is
Fabaceae
largest and outermost. flower

Androecium: 3rd whorl of the flower/
male whorl
 It is composed of stamens.
 Each stamen has a slender stalk, at the
top an anther connected by a connective.

Anther
Connective

Filament

Adelphy: Fusion of filaments &
anthers free
 Monadelphous: The filaments of all the
stamens become fused forming a single
bundle.
 Diadelphous: Here the filaments are fused
forming two bundles.
 Polyadelphous: The filaments of the stamens
are fused forming many bundles.
Monadelphous Diadelphous Polyadelphous

Pea

Hibiscus Citrus

Syngeny: Fusion of anthers and
filaments free.
 Syngenesious stamens: The anther lobes of
all the stamens become fused and filaments
are free.
 Synandry: Here both filaments and the
anthers are fused.
Syngenesious stamens Synandr
y

Fused anthers Fused anthers
and filaments
Free filaments

 Epipetalous stamens: Here the filaments
of stamens are found attached to the
petals

Anther lobes:
 Monothecous: The anthers have only one
lobe

 Dithecous: The anthers have only two
lobe

Gynoecium: 4th whorl of the flower/
female whorl
 Gynoecium is composed of carpels
 Each carpel has three parts, Ovary with
ovules, Style and Stigma.

Types of Gynoecium:
 Apocarpous: Here the gynoecium consists
of two or more carpels and all the carpels
are free.

 Syncarpous: Here the gynoecium consists
of two or more carpels and all the carpels
are fused.

 Monocarpellary Gynoecium: A gynoecium
with a single carpel
 Bicarpellary Gynoecium: A gynoecium
with two carpels
 Tricarpellary Gynoecium: A gynoecium
with three carpels
 Tetracarpellary Gynoecium: A gynoecium
with four carpels
 Pentacarpellary Gynoecium: A gynoecium
with five carpels
 Polycarpellary Gynoecium: A gynoecium
with more than five carpels

Types of gynoecium based on
locules
 Unilocular ovary: Ovary having single
chamber Eg. Pea
 Bilocular ovary: Ovary having two
chambers Eg. Brinjal
 Trilocular ovary: Ovary having three
chambers Eg. Castor
 Tetralocular ovary: Ovary having four
chambers Eg. Ocimum
 Pentalocular ovary: Ovary having five
chambers Eg. Hibiscus

Types of gynoecium based on
locules

Placentation: The arrangement of
ovules on the placenta inside the
ovary is called placentation. There
are several types of placentation.
 a. Marginal placentation
 In this type, the ovary is
monocarpellary, monolocular and the
placenta is on the ventral suture. The
ovules are attached to the placenta which
is on the margin. e.g. Beans, Pea, etc.

 b. Axile placentation :
 In this type, the ovary has two or more
carpels, syncarpous, and has two or more
locules. The ovules are borne at or near the
centre on the axis formed by the union and
fusion of the septa (partitions) and usually in
vertical rows. e.g., Apple, Hibiscus etc.

 c. Parietal Placentation:
 In this type, the ovary has two or more carpels,
and is syncarpous, and monolocular. Here there
are as many placentae as the number of
carpels
and the ovules are attached to those placentae
at the periphery. e.g., Cucurbita, Argemone.

 d. Free Central placentation:
 In this type the ovary is
monolocular, wherein the ovules are borne
on a central axis that reaches the top of
the ovary. e.g., Primula, Sandal Wood.

 e. Free basal placentation:
 Similar to free central but the placental
column does not reach the top of the
ovary. e.g., Portulaca, Celosia

Structure of mature anther:
 Anther Wall Layers : Anther wall consist of following layers :
 (1) Epidermis : Outermost, single layered and protective in function. The
epidermis of Arceuthobium develops some fibrous thickenings and is
called exothecium.
 (2) Endothecium : Cells of this layer have a-cellulosic fibrous bands
arising from inner tangential wall which help in dehiscence of anther due
to their hygroscopic nature.
 (3) Middle layer : Cells of this layer are ephemeral and are one-three
layered. It degenerates at maturity.
 (4) Tapetum : This is the innermost layer of anther wall which surrounds
the sporogenous tissue. Tapetal cells are nutritive. The tapetum has two
types of cells:
 (a) Secretory or glandular tapetum : These cells secrete sporopollenin
which help in the ornamentation of exine.
 (b) Amoeboid or plasmodial or invasive tapetum : Cells undergo
breakdown and their entire protoplasts move in the centre to nourish
microspores.

Structure of mature anther:
 Pollen sac (Microsporangium): an anther
consists of two lobes. Each lobe has two
cavities called pollen sac or microsporangia. A
matured microsporangia consists of large
number of pollen grains.

Structure of pollen grain:

 The branch of science that deals with the
study of the characteristics of the pollen
grains is called palynology.
 Each pollen grain is a haploid, unicellular
mass of protoplast with a single nucleus.
 It is surrounded by a thick wall differentiated
into two layers; the outer thick exine and the
inner thin intine.
 The pollen grains reveal a wide range of
microsculpturing of the exine.
 At one or more places, the exine is very thin
or absent. These spots are called germ
pores

Ovule:
 Ovule: It is defined as integumented
megasporangium present within the ovary
that develops into a seed.
 Funicle is the stalk that attaches ovule at
maturity to the placenta.
 The place of attachment is Hilium.
 The mass of parenchyma cells forming the
main body of ovule is the Nucellus.
 The basal part of the nucellus is called
chalaza.

Ovules
 The nucellus is covered by one or two
envelopes called integuments.
 At the tip the integuments leave an
opening called Micropyle.
 Embeded in the nucellus is embryo sac or
female gametophyte containing eight
nuclei.
 They are egg nucleus with two synergids
towards micropyle, three antipodals near
chalazal end and two polar nuclei at the
center.

Types of Ovules:
 (1) Orthotropous : The micropyle, chalaza and funicle are in
a straight line. This is the most primitive type of ovule
e.g., Piper, Polygonum, Cycas.
 (2) Anatropous : The ovule turns at 1800 angle. Thus it is
inverted ovule. Micropyle lies close to hilum or at side of
hilum e.g, found in 82% of angiosperm families.
 (3) Campylotropous : Ovule is curved more or less at right
angle to funicle. Micropylar end is bend down slightly
e.g., in members of Leguminosae, Cruciferae.
 (4) Hemianatropous : Ovule turns at 900 angle upon the
funicle or body of ovule and is at right angle to the funicle
e.g., Ranunculus.
 (5) Amphitropous : Ovule as well as embryo sac is curved
like horse shoe e.g, Lemna, Poppy, Alisma.
 (6) Circinotropous : The ovule turns at more than 3600
angle, so funicle becomes coiled around the ovule
e.g., Opuntia (Cactaceae), Plumbaginaceae.

Study of angiosperm flower

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Study of angiosperm flower