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REPRODUCTIVE ORGANS
Flower
•Flower is the structure concerned with sexual reproduction,
consisting of the androecium (male organs: stamens) and
gynoecium (female organs: carpels), commonly surrounded by
sterile corolla (petals) and calyx (sepals).
Flower and reproduction
•Flower is composed of 4 groups of modified leaves: sepals, petals, stamens
and carpels.
•Sepals are the outer floral leaves, usually greenish, which are borne in a tight
spiral or whorled. They form calyx which protects flower (forming buds) before
opening. Sepals can be separate or fused. Sometimes calyx is persistent and
accompanies fruit after fertilization.
•Petals are the inner floral leaves, usually brightly coloured or smelling to
attract pollinators, and borne in a tight spiral, or whorled. They form corolla
which encloses the reproductive organs and, together calyx, protects them.
Petals can be separate or fused. After fertilization petals fall down.
•Stamens are fertile leaves (sporophylls) forming the male organs comprising
a stalk (the filament) and the anthers which are commonly 2-lobed. Anthers
contain microsporangia that produce microspores giving rise to male
gametophytes.
•Carpels are fertile leaves (sporophylls) forming the female organs comprising
an ovary (containing 1 to many ovules borne on a placenta) and with a usually
terminal style tipped by the stigma. Ovules contain megasporangia that
produce megaspores giving rise to female gametophytes (embryo sac).
Structure of flowers
PERFECT or MONOCLINOUS
(BISEXUAL)
IMPERFECT or DICLINOUS
(UNISEXUAL)
Stamens and carpels occur in
the same flower
Stamens or carpels in separate
flowers in the same plant
MONOICIOUS PLANT
DIOICIOUS PLANT
Plant with bisexual flowers, or
alternatively with both stamen and
carpels in flowers in the same individuals
Flowers with stamens and
carpels in separate individuals
COMPLETE
INCOMPLETE
With sepals, petals, stamens and
carpels in the same flower
Lack of one or more floral parts
Floral symmetry
Regular flowers
(Actinomorphic)
Irregular flowers
(Zygomorphic)
Similar elements of whorls, with
radial symmetry, i.e. divisible into
equal halves in many planes
Different element of whorls, with
bilateral symmetry, i.e. divisible into
equal halves in only 1 plane
Morphology of
calyx and corolla
Morphology of
calyx and corolla
Origin of the carpel from a reproductive leaf
(sporophyll)
•A leaf bearing megasporangia folded in order to protect them.
Inflorescences
Monopodial or indefinite
(lateral floral branches arise from
a main, central axis)
•Raceme or cluster
•Spike (spadix, catkin)
•Corymb
•Umbel
•Capitulum
Sympodial or definite or
cymose
(apparent main axis made up of
many lateral floral branches,
each arising from the one before)
•Monochasium
•Dichasium
Compound (main axis with lateral branches bearing
the same or a different type of inflorescence)
•Panicle or compound raceme
•Compound umbel
•Polychasium
•Spikelet or compound spike
•Cluster of capitula
•Cluster of spikes
Inflorescences
panicle
composite umbel
spike
raceme
corymb
helicoid
monochasium
dichasium
scorpioid
monochasium
spadix
umbel
capitulum
polychasium
•Monopodial or indefinite
inflorescences
•Compound and definite inflorescences
Monopodial inflorescences
•Raceme: the main axis continues to grow, producing flowers laterally
with pedicels.
•Spike: a raceme in which the flowers are all sessile; is characteristic of
Poaceae.
•Corymb: a racemose inflorescence in which the lower pedicels are
longer than the upper so that the flowers lie as a dome, or dish, and
the outline is roundish or flattish.
•Umbel: all the pedicels arise at the apex of an axis. It is commonly
compound, usually umbrella-shaped, and is characteristic of Apiaceae.
•Capitulum: consists of closely packed flowers or florets which have no
stalks and arise on a flattened axis, all at the same level. It is
surrounded by an involucre of bracts giving it the appearance of a
single flower. Capitula are typical of Asteraceae.
Cymose and compound
inflorescences
•Monochasium: consists of a single floral branch bearing flowers and ending
in a single terminal flower (e.g. scorpioid and helicoid cymes).
•Dichasium: each branch give rise to two more branches.
•Polychasium : each branch give rise to many more branches.
•Panicle: a compound raceme, i.e. one that comprises several racemose parts;
it is characteristic of Poaceae.
•Compound umbel: an umbel in which the pedicels give rise to other umbels.
•Spikelet or compound spike: a spike in which short branches give rise to 2-3
spikes; it is characteristic of Poaceae.
•Cluster of capitula: a racemose inflorescence in which the pedicels give rise
to many capitula.
•Cluster of spikes: a racemose inflorescence in which the pedicels give rise to
many spikes.
Inflorescences
Inflorescences
Inflorescences
•Capitulum: consists of closely packed
flowers or florets (disc and ray florets)
which have no stalks and arise on a
flattened axis, all at the same level. It is
surrounded by an involucre of bracts
giving it the appearance of a single flower.
Capitula are typical of Asteraceae.
Inflorescences
Capitulum of thistle with
only tubular, disc florets
Capitulum
of
dandelion
with
only ligulate, ray
florets
Capitulum
of
sunflower
with
both tubular and
ligulate florets
Inflorescences
•Compound umbel: all the pedicels arise at the apex of an
axis; each pedicel gives rise to one umbel. It is characteristic of
Apiaceae.
Inflorescences
simple umbel
compound umbel
Inflorescences
•Spikelet is typical of Poaceae.
Inflorescences
•Panicles of Zea mays
Development
of
gametophytes
sporogenesis
gametogenesis
Stamens
•Stamen is the male organ of a
flower, comprising a stalk (the
filament) and the anther which is
commonly 2-lobed, each lobe
containing 2 pollen sacs
(microsporangia) in which
microsporocytes undergo 2 meiotic
divisions to produce 4 microspores
that become pollen grains.
immature pollen grain
Pollen grain
•Pollen grain derives from germinating microspore. It contains the
male gametophyte, a structure made up of the pollen grain plus a
pollen tube. The grain contains 3 haploid nuclei (a tube nucleus and 2
sperm nuclei).
Pollen grain
• Pollen grain (20-250 μm) is protected by
an outer envelope called exin (composed
of sporopollenin) showing various types
of sculptures (taxonomic value), and by an
inner envelope called intin (composed of
cellulose and pectins). It bears stretched
or circular openings from which the pollen
tube comes out. They are known as solcus
and porus.
• Pollen grains are an important source of
nutrients for animals and insects (rich of
starch and lipids).
• They are frequent in fossils.
Various kinds of pollen grains at SEM
Carpel
•Carpel is the female reproductive organ
of the flower, i.e. a unit of the gynoecium,
comprising an ovary (containing 1 to many
ovules borne on a placenta) and with a
usually terminal style tipped by the
stigma.
•Style is an extension of the carpel which
supports the stigma.
•Stigma is the part on which pollen grains
germinate.
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Pollination and pollen
tube formation
•Stigma is the part on which
pollen grains germinate through
absorption of water and
consequent formation of the
pollen tube.
•Angiosperms have a stigmatic
pollination.
Pollination and pollen
tube formation
•The pollen grain contains 3 haploid nuclei
(a tube nucleus and 2 sperm nuclei), which
pass down the tube to the ovum. One of
the sperm nuclei fertilizes the ovum, and
the second fuses with the 2 polar nuclei
forming the endosperm. The tube nucleus
(which is considered to be vestigial, having
been completely functional earlier in the
evolution of flowering plants) degenerates
after double fertilization (so called because
of the two unions of nuclei).
•With the appearance of flower,
angiosperms have solved the
problem
related
to
the
impossibility to move towards a
reproductive partner.
•Flower assures a high rate of
cross pollination.
•Pollination is the transfer of pollen grains (containing male
gametophytes) from the anther to the stigma of a flowering
plant. Flowers and insects have co-evolved.
•Rosemary’s anthers depositing white pollen
grains on hairy back of a bee.
•Flowers pollinated by bees are yellow or blue since
these insects are not sensitive to red wavelenghts.
•Flower of Digitalis with tubular
corolla showing inside some stains
acting as landing platform for bees.
•Flowers of the genus Ophrys
(Orchidaceae), miming the shape
of a female bee, attract male
pollinators.
•Nectars are an important feeding source for
pollinators. They are secretory structures
producing energetic nutrients.
•Flowers pollinated by birds are often of red colour.
•Graminae have an anemophilous
pollination: hairy stigmas get pollen
grains from hanging anthers.
•Wind-pollinated plants do not
depend on insects so that they do not
spend energy for nectar production,
and are colourless and odourless.
•Anemophilous pollination is less
efficient and succeeds only when a
high number of individuals of a
population stay close each other (no
farther than 100 m).
•Some aquatic angiosperms are pollinated by water.
•The most important pigments for the colour
of flowers are flavonoids (mainly
anthocyanins) and carotenoids.
•Fertilization involves the fusion of two haploid nuclei from two
distinct individuals (cross-fertilization) or from one individual (selffertilization).
•Normally male and female organs of a flower mature at different
times (dichogamy), or alternatively they are physically separated in
order to favour cross-fertilization.
•Plants with self-pollination have small, colourless flowers
since they do not need to attract pollinators.
•Self-pollinated populations have a low level of genetic
variability.
•Self-pollination is favoured in some cases (e.g. disturbed
areas where pollinators are rare).
Female gametophyte and double fertilization
•The female gametophyte, known as embryo sac, is
an oval structure in the nucellus of the ovule of
flowering plants, formed by the division of the
haploid megaspore nucleus (which is produced by
the only diploid cell undergoing meiosis in the
megasporangium), and the site of fertilization of the
egg and development of the embryo.
•It consists of 6 haploid cells without cell walls (2
synergidae, 3 antipodal cells, and an egg cell) and 2
haploid nuclei (polar nuclei). Sometimes the 2
haploid, polar nuclei fuse to form a single,
endosperm mother cell. At fertilization, 1 male
nucleus fuses with the egg nucleus to form a zygote
which develops into the embryo. The second male
nucleus fuses with the primary endosperm nucleus
to form the endosperm nucleus. This then divides to
form the endosperm.
Double fertilization
•It occurs only in angiospermes and is the production of 2 sperm nuclei,
both of which contribute to fertilization.
•The male gametophyte, comprising the pollen grain and pollen tube,
contains 2 sperm nuclei and 1 vegetative nucleus.
•The vegetative nucleus degenerates once the pollen tube has penetrated
the embryo sac by micropyle.
•The 2 sperm nuclei enter the embryo sac. One unites with the egg nucleus
to form the zygote, which develops into the embryo. The other unites with
both of the polar nuclei or with the nucleus formed by their fusion, to form
the primary endosperm nucleus, from which endosperm develops.
•Endosperm is a triploid tissue storing food materials which are broken
down during seed germination.
•Double fertilization assures endosperm development just in the case of egg
cell fertilization, avoiding the waste of nutritive substances.
Double fertilization
Seed
•Seed of angiosperms is composed of 2
diploid generations (the outer
integuments and the embryo) and one
triploid generation (endosperm).
•Embryo has usually 1 or 2 cotyledons.
•Endosperm functions as storage of
nutrients (carbohydrates, proteins, lipids)
for embryo and seed germination.
•Seed nutrients are stored in the vacuole
or leucoplasts of endosperm cells.
Life cycle of an angiosperm
Fruit
• After fertilization, ovule is transformed into seed,
ovary into fruit.
• Fruits protect quiescent seeds and contribute to their
dispersal.
Fruit
• Ovary walls known as pericarp,
thicken and differentiate into 3
layers: the inner endocarp, the
middle mesocarp and the outer
exocarp. These layers are usually
more evident in fleshy fruits.
Classification of fruits
origin
AGGREGATE
SIMPLE
MULTIPLE
formed by the joining of several
carpels that were separate in
the flower (e.g. Rubus).
formed from a single carpel
or from various fused carpels
formed from
inflorescence
pineapple)
dehiscence
INDEHISCENT remaining closed at
DEHISCENT (many-seeded, dry)
maturity
opening naturally at maturity
follicle, legume, lomentum, siliqua,
capsule, schizocarp
consistence
FLESHY (one or
more seeds)
berry, drupe, pome
DRY (one seed)
samara, nut, achene,
caryopsis
an entire
(e.g.
fig,
Classification of fruits
TRUE
Strictly, the ripened
ovary of a plant and its
contents
FALSE
When the ripened ovary
and seeds are combined
with other structures; e.g.
the apple (a pome) in which
the true fruit (core) is
surrounded by flesh derived
from the floral receptacle.
Fleshy fruits
• Drupe: a fleshy indehiscent fruit containing one or a few
seeds, each enclosed within a stony endocarp, as in the genus
Prunus (Rosaceae).
Fleshy fruits
• Berry: a fleshy, indehiscent, fruit containing many seeds
immersed in a pulp (endocarp+mesocarp); they do not have
hard parts except the seeds (e.g. grape, tomatoes, blueberry,
currant, banana, avocado, pepper, eggplant, belladonna).
Fleshy fruits
• Hesperidium: a berry in which the fleshy part is divided into
segments and the outer skin is a tough, glandular leathery
rind, e.g. Citrus (Rutaceae such as orange, lemon etc.).
Fleshy fruits
• Pepper: a berry, typical of Capsicum where the fleshy
pericarp surrounds a hollow containing many seeds.
Fleshy fruits
• Pepo: a unilocular, many-seeded, hard-walled berry that
forms the fruit of Cucurbitaceae (e.g. marrow, melon,
watermelon, cucumber etc.).
Fleshy fruits
• Sorosis: a fleshy, aggregate fruit (e.g. mulberry, currant etc.);
strawberry is an aggregate, false fruit, where the pulp
originates from receptacle while the true fruits are achenes.
Fleshy fruits
(enlargement of
the receptacle)
• Pome: fruit in which the seeds are protected by a tough carpel wall
and the entire fruit is embedded in a fleshy receptacle; in the
apple, the carpel wall surrounding the seeds comprises the core,
which is the fruit, the edible fleshy part of the apple being the
receptacle.
Fleshy fruits
• Syncarp: a fleshy, multiple fruit formed from an
inflorescence, often including bracts, as in pineapple.
Ripening
immature
• Ripening is a stage in the
development of fruit, characterized
by the softening, colouring, and
sweetening of the tissue, and by a
decrease in acidity. Often this is
associated with an increase in the
rates of respiration, cell expansion,
and ethylene production, combined
with a loss of chlorophyll.
• The colour change is a signal for the
seed dispersors.
ripening
Ripening
• Red colour is dominant among ripe fruits since
animals, that are sensitive to red wavelenghts, are
the best seed dispersors.
Dry fruits
• Follicle: a dry fruit derived from a single
carpel, containing more than one seed,
which dehisces along one side (along the
suture) only.
• Siliqua: the capsular fruit of the
Brassicaceae when at least three times as
long as broad, containing many seeds
attached to a central outgrowth known as
replum; it dehisces along dorsal and ventral
sides (sutures).
Dehiscent fruits
• Capsule: a dry, dehyscent fruit
formed from a syncarpous
ovary; it contains many seeds
and opens in different ways.
Dehiscent fruits
• Legume or pod: a two-valved
fruit formed from a single
carpel, usually severalseeded and usually opening
along dorsal and ventral
sides, typical of Fabaceae.
Dehiscent fruits
• Lomentum: a fruit derived
from a single carpel which
breaks up into one-seeded
portions, as in carob tree
and tamarind.
Dehiscent fruits
• Schizocarp: a fruit derived from a
syncarpous ovary which breaks up at
maturity into one-seeded portions
(mericarps), as in most members of
Lamiaceae (4 mericarps) and Apiaceae
(2 mericarps).
Indehiscent fruits
•Samara: a dry, indehiscent, winged
1- or 2-seeded (double samara) nut
or achene, characteristic of the
genus Fraxinus and Acer.
•Achene: a small, dry, oneseeded, indehiscent fruit,
strictly of one carpel.
Indehiscent fruits
• Cypsela: a small, dry, one-seeded, indehiscent fruit formed
from two united carpels, normally accompained by pappus,
as in the Asteraceae. Sometimes treated as a form of achene.
Indehiscent fruits
• Nut: a dry, one-seeded,
indehiscent fruit with a woody
pericarp (e.g. acorn, hazelnut,
walnut); the seed is not united to
the pericarp.
Indehiscent fruits
• Caryopsis: a dry, one-seeded, indehiscent fruit, characteristic
of grasses (Poaceae), having the pericarp united to the seed;
the grain of a cereal grass.
Fruit dispersal
•Fruits of devil’s claw with hooks
joining to fur coat of animals.
Pharmaceutical importance of
fruits and seeds
•The following fruits are used in pharmaceutical
preparations: papaya, orange and citrus, anise, star
anise, capsicum, senna.
•Several plants provide seed containing oils to be used
in pharmaceutics: rape, linseed, cotton, castor, coconut,
sesame, etc.
•Other seed used in pharmaceutics are: coffee, cocoa,
sweet and bitter almond, walnut, hazelnut, chestnut etc.