ANGIOSPERMS
GENERAL CHARACTERISTICS
• Enclose their seed in masses of tissue = fruit
– Fruit protects and aids in the distribution of seeds
• Their xylem is more specialized and transports
water and minerals more efficiently
• Found in nearly every habitat
Why Sucessful
• Have evolved mechanisms for dispersal of
both pollen and seeds
– Pollen Dispersal – co-evolution of flowers that
provide nectar which increases the probability of
successful pollination
– Seed Dispersal- co-evolution for fruits covering
seeds which increases distance of seed dispersal
from the parent plant
THE TWO SUBCLASSES
MONOCOTS AND DICOTS
• MONOCOTS include corn, wheat, lilies,
daffodils, orchids, and palms
• DICOTS include roses, clover, tomatoes, oaks,
and daisies
• There are several differences between these
two groups:
Sexual Reproduction in Angiosperms
Most are terrestrial and all lack locomotion.
This poses several problems.
• Gametes are delicate single cells. For two plants to
cross fertilize, there must be a mechanism for the
two gametes to reach each other safely.
• There must also be a mechanism to disperse their
offspring far enough away from the parent so that
they do not have to compete with the parent for
light, water, and soil minerals.
The functions of the flower solve both of these
problems.
The Flower and Its Pollination
• In angiosperms, meiosis in the sporophyte
generation produces two kinds of spores.
• microspores
o which develop in the microsporangium and
o which will germinate and develop into the male
gametophyte generation and
• megaspores
o which develop in the megasporangium and
o which will develop into the female gametophyte
generation.
TYPES
Both types of sporangia are formed in flowers.
• In most angiosperms, the flowers are perfect: each
has both microsporangia and megasporangia.
• Some angiosperms are imperfect, having either
microsporangia or megasporangia but not both.
– Monoecious plants have both types of imperfect flower on
the same plant.
– Dioecious plants have imperfect flowers on separate plants;
that is, some plants are male, some female. Examples
include willows, poplars, and the date palm.
Parts of the Flower
•stamens in which the microsporangia form
•carpels in which the megasporangia form.
Stamens
• Each stamen consists of a
• lobed anther, containing the microsporangia and
supported by a thin filament
• Meiosis of the diploid microspore mother cells in
the anther produces four haploid microspores.
Each of these develops into a two-celled pollen
grain.
Carpels
•
•
•
•
•
Carpels consist of a
stigma, usually mounted at the tip of a
style with an
ovary at the base.
Often the entire whorl of carpels is fused into a
single pistil.
• The megasporangia, called ovules, develop within
the ovary.
Pollination
• When a pollen grain reaches the stigma, it
germinates into a pollen tube.
• The generative nucleus divides by mitosis forming 2
sperm nuclei.
• These, along with the tube nucleus, migrate down
the pollen tube as it grows through the style and into
the ovule chamber.
• The pollen tube with its contents makes up the
mature male gametophyte generation.
Double fertilization
• The pollen tube enters the ovule
• One sperm nucleus fuses with the egg forming the
diploid zygote.
• The other sperm nucleus fuses with the polar nuclei
forming the endosperm nucleus. Most angiosperms
have two polar nuclei so the endosperm is triploid
(3n).
– Endosperm is the FOOD for the developing embryo and is
part of the seed
• The tube nucleus disintegrates.
Self-incompatibility
• Most angiosperms have mechanisms by which
they avoid self-fertilization.
Fruits
• Fruits are a development of the ovary wall and sometimes other flower
parts as well.
• Fruits promote the dispersal of their content of seeds in a variety of
ways.
– Wind. The maple "key" and dandelion parachute are examples.
– Water. Many aquatic angiosperms and shore dwellers (e.g., the coconut palm)
have floating fruits that are carried by water currents to new locations.
– Hitchhikers. The cocklebur and sticktights achieve dispersal of their seeds by
sticking to the coat (or clothing) of a passing animal.
– Edible fruits. Nuts and berries entice animals to eat them. Buried and forgotten
(nuts) or passing through their g.i. tract unharmed (berries), the seeds may end
up some distance away from the parent plant.
– Mechanical. Some fruits, as they dry, open explosively expelling their seeds. The
pods of many legumes (e.g., wisteria) do this.
Link to Short Video’s in Cool Angiosperm Adaptations http://www.youtube.com/watch?v=igkjcuw_n_U&list=PLCC07E66503F99BB5