Origin of the Angiosperms: the
flowering plants

The origins of the angiosperms are not clearly
worked out yet.

Oldest fossils from about 125 mya.

The sister group of the angiosperms appears to
be the Gnetophytes.

Some have leaves similar to Angiosperms as
well as fleshy berrylike fruits. Also have doublefertilization.
Ephedra
Gnetophytes
 90
species,
3 genera
 Double
fertilization
 Transition to
angiosperms?
Welwitschia
Gnetum
Angiosperms
 The
name Angiosperm (from the Greek
word Angion meaning a container) refers
to the fact that seeds are contained within
fruits.
 Only Angiosperms
produce fruits.
have flowers and
Angiosperms
 There
are about 235,000 species of
Angiosperms and these divide into two
main groups the monocots and the dicots.
 The
monocots have one cotyledon or
“seed leaf” in the embryo and the dicots
have two cotyledons. There are also other
differences.
Monocts vs dicots

Monocot
 One cotyledon
 Veins usually parallel
 Vascular tissue scattered
 Root system fibrous
 Pollen grain 1 opening

Floral organs usually in
multiples of three.

Dicot
 Two cotyledons
 Veins usually netlike
 Vascular tissue in a ring
 Taproot
 Pollen grain has 3
openings
 Floral organs usually in
multiples of four or five
Monocots
 About
25% of angiosperms are monocots.
These include:




Orchids
Lilies
Grasses
Palms
Dicots
 About
2/3 of all angiosperms are dicots.
 These include:




Oaks
Maples
Roses
Peas
Structure of the flower

The flower is a structure specialized for sexual
reproduction.

Flower is a specialized shoot with up to four
rings of modified leaves called floral organs:




Sepals
Petals
Stamens
Carpels
Structure of the flower
 Sepals:
usually green, enclose flower
when in bud.
 Petals:
brightly colored and attract
pollinators.
Stamens
 Stamens:
produce microspores that give
rise to pollen which contains male
gametophyte.
 Stamen
includes the anther where pollen
is produced and a stalk called the filament.
Carpels
 Carpels
produce megaspores that produce
female gametophytes.
 Tip of carpel has a sticky stigma that
receives pollen
 Style leads to ovary at base that contains
ovules.
 Fertilized ovules develop into seeds.
Life Cycle in Angiosperms
 Pollen
grains are carried by the wind (e.g.
in grasses) or by pollinators (such as
insects, birds, or bats) to the sticky stigma
at the top of a carpel.
 Pollen
grain contains the male
gametophyte. Male gametophyte
produces two sperm and a structure called
the pollen tube.
Life Cycle in Angiosperms
 When
pollen lands on stigma it germinates
and the pollen tube grows down the style
to reach the ovary.
 The
ovary at the base of the carpel
contains the ovules, which contain the
female gametophyte, which produces an
egg.
Life Cycle in Angiosperms
 The
pollen tube enters the ovule and
releases two sperm cells.
 One
sperm cell fertilizes the egg.
 What
does the other sperm do?
 Do you remember double-fertilization?
Life Cycle in Angiosperms
 The
second sperm fuses with the large
central cell of the female gametophyte,
which contains two nuclei forming a triploid
cell.
 This
triploid cell then divides repeatedly to
form the endosperm, which contains
starch and other food reserves
Life Cycle in Angiosperms
 After
double fertilization, the ovule
develops into a seed.
 The
endosperm is food reserves for the
sporophyte embryo, which develops from
the fertilized egg.
Life Cycle in Angiosperms

As the seeds develop from ovules, the wall of
the ovary becomes thicker and develops into a
fruit.

Thus, a fruit is a mature ovary that contains
seeds and every fruit was a flower.

The outer fleshy part of a fruit doesn’t feed the
seed. It’s purpose is to attract animals that will
eat it and later disperse the seeds.
Seed dispersal
 Various
fruits also have other adaptations
that help to disperse the seeds.
 These
include wings or parachutes to
enable the seed to float away from its
parent, barbs to hook onto passing
animals, and the ability to float on water.
Types of seed dispersal
 Wind
 Water
 Mechanical
 Biotic
(by animals)
Types of seed dispersal
Wind
Adaptations for flight:
Tiny, dustlike seeds (ex. Orchids)
Types of seed dispersal
Wind
Adaptations for flight:
Wings!
Types of seed dispersal
Water
Adaptations for buoyancy:
Air space!
Types of seed dispersal
Mechanical
Adaptations for explosion:
Geranium
mistletoe
Types of seed dispersal
Biotic
Adaptations for attachment:
Harpagophytum
Types of seed dispersal
Biotic
Adaptations for attachment:
Bidens
Types of seed dispersal
Biotic
Adaptations for ingestion:
Types of seed dispersal: biotic
 Biotic




adaptations of fruits for ingestion
Fleshy
Taste good (nutritious)
Brightly colored
Seeds can survive passage through the gut
Plant-animal associations
Seed dispersal
Coevolution
Plant-animal associations
Animal evolution
Coevolution
Plant evolution
Alliances that have influenced the evolution of both
partners
SELECTION PRESSURE APPLIED BY BOTH PARTIES
Pollination
 Pollination
is the transfer of pollen to
stigmas of flowers to achieve fertilization.
 About
10% of angiosperms are wind
pollinated and almost all others are
pollinated by animals (biotic pollination)
 The
flower is an adaptation to increase the
efficiency of biotic pollination.
Wind Pollination

Used by grasses, and many trees such as
birches, oaks, willows.

The advantage of wind pollination is that no
resources are expended on producing flowers.

The main disadvantage is that the direction,
distance and delivery of pollen is uncertain.
Pollination - wind
Biotic Pollination

Many Angiosperms have coevolved close
relationships with their animal pollinators.

In some cases a single plant is pollinated
exclusively by a single species of animal.

More often certain groups of plants have
coevolved to be pollinated by certain groups of
pollinators e.g. bees, moths, or birds.
Biotic Pollination
 Pollination
by animals requires plants to
advertise themselves to attract pollinators
and reward their pollinators for visiting
them.
How plants attract pollinators
 Flowers
use color and shape to advertise
themselves.
How plants attract pollinators
 Plants
also use scent. Plants produce a
general “flowery” scent, but some also
mimic scents such as dung, rotting meat
or insect pheromones to fool pollinators
into visiting them.
How plants reward (bribe)
pollinators
 Rewards
offered include nectar, pollen and
oils.



Nectar is a solution of sugar and amino acids.
Pollen is rich in protein (16-60%) and lipids (310%)
Oils have twice the calories of carbohydrates.
Pollination Syndromes
 Selection
has favored plants that possess
traits attractive to certain pollinators.
 This
has led to the evolution of pollination
syndromes the coordination of traits of
plants and their pollinators.
Pollination Syndromes

Pollination Syndromes have developed between
certain flowers and





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Bees
Beetles
Moths
Butterflies
Carrion flies
Birds
Flying Mammals
Non-flying mammals
Examples of Pollination
Syndromes: Butterflies
 Flowers




that attract butterflies have:
a landing platform
usually blue, purple, deep pink or red flowers
fragrant flowers with a light scent
nectar often located in deep tubes
Examples of Pollination
Syndromes: Moths
As for butterflies, flowers that attract moths also
often have:



a landing platform and
nectar in a narrow deep tube
But unlike them:



flowers are usually white
open at night
are fragrant with a heavy musky scent
Examples of Pollination
Syndromes: Carrion flies

Unlike flowers that attract butterflies and
moths those that attract carrion flies
depend on fooling their pollinators.

These plants:



are colored to resemble dung or carrion
produce heat or foul odors
provide no nectar or pollen reward
Examples of Pollination
Syndromes: Birds

Flowers that attract vertebrates such as birds
and bats rather than insects must be larger
and contain a greater reward.

Thus flowers that attract birds:





are large and damage resistant
have lots of nectar in tubes
usually red or other bright colors
open during the day
not fragrant (most birds have a poor sense of smell)
Examples of Pollination
Syndromes: Bats

Bats are large and not such adept fliers as birds
so flowers designed to attract them



Contain lots of pollen and nectar
And are held away from the plant for easy access
Because bats, like moths, mainly forage at night
flowers that evolved to attract them have some
similar traits to those that attract moths



open at night
are light colored
have a strong odor
Human uses of
Angiosperms
Food Plants
The Big Six
 80%
of the total calories consumed by
humans come from 6 crops
The Big Six
 80%
of the total calories consumed by
humans come from 6 crops

Wheat
Triticum aestivum
The Big Six
 80%
of the total calories consumed by
humans come from 6 crops


Wheat
Rice
Oryza sativa
The Big Six
 80%
of the total calories consumed by
humans come from 6 crops



Wheat
Rice
Corn
Zea mays
The Big Six
 80%
of the total calories consumed by
humans come from 6 crops




Wheat
Rice
Corn
Potatoes
Solanum tuberosum
The Big Six
 80%
of the total calories consumed by
humans come from 6 crops





Wheat
Rice
Corn
Potatoes
Sweet potatoes
Ipomoea batatas
The Big Six

80% of the total calories
consumed by humans
come from 6 crops
 Wheat
 Rice
 Corn
 Potatoes
 Sweet potatoes
 Manioc/Cassava
Manihot esculenta
The “Other Eight”
14 plant species =
majority of human calories








Sugar cane
Sugar beats
Beans
Soybeans
Barley
Sorghum
Coconuts
Bananas