Transcript Lecture 10, Angiosperms - Cal State LA

# of families
Evolution of Plant Biodiversity
Seedless
vascular
plants
Gymnosperms
dominate
Angiosperms
First
gymnosperms
Mackenzie 2003
Phylum Anthophyta, Angiosperms
(Flowering plants)
250,000 species named to date
Key Angiosperm features
“Angion” = container, “sperm” = seed
Advanced transport tissues
tracheids + vessels in xylem tissue, wide channels for
moving water
Flowers + pollination syndromes
more efficient reproduction: deliver your pollen to eggs
of your own species
Protected seeds inside fruit
provides means of dispersal for offspring, via animals
that eat fruit, or wind, or water
Key Angiosperm features
“Angion” = container, “sperm” = seed
Advanced transport tissues
tracheids + vessels in xylem tissue, wide channels for
moving water
tracheids have an extra, outer cell wall re-inforced with lignin, a
super-strong material that allows stems of plants to stand upright
- there are holes in the lignin wall to allow water to flow from one
to the next
- cells are dead by the time they function in water transport
- wood is basically just lots of tracheids pressed together
Tracheids and vessel elements
Gymnosperm xylem tissue contains
only tracheids
Angiosperm xylem contains both
tracheids and vessel elements
Tracheids = elongated single cells that
transport water in the xylem tissue
- pass water cell-to-cell
Vessel elements = wider vessels

Tracheids and vessel elements
Understand the progressive adaptations to life on dry land
that culminated in the super-successful angiosperms
p. 639
Reproductive structures of seed plants
Gymnosperms
Angiosperms
Flower
Pistil/Carpel(s)
Stamen
Petal
Sepal
Tip of stamen is the anther, which contains
the microsporangia
produce microspores
grow into pollen grains,
housing male gametophyte
(only 2 cells big!)
Anther releasing pollen grains
(after meiosis)
Base of carpel = ovary, protective structure that contains ovules
the megaspore inside each ovule
grows into the female
gametophyte
1 egg nucleus
2 polar nuclei, which will
become the endosperm
Double Fertilization
Pollen grain has 2 cells
1 grows into pollen tube,
penetrates ovary
other 1 forms 2 sperm:
sperm #1 fertilizes egg
sperm #2 fuses with
both polar nuclei to
form the endosperm
(3N, triploid)
Endosperm becomes
food for the growing
embryo
Double Fertilization
Each ovule is initially
surrounded by two
integuments
After fertilization, these
become the hardened
seed coat
The whole ovary wall
then thickens into the
pericarp, the thick
outer wall of the fruit
Ovule becomes seed, ovary becomes fruit
Campbell & Reece 2002
Angiosperm seeds aren’t exposed
like naked gymnosperm seeds
Instead, they are protected by a
ripened ovary wall (pericarp),
sometimes with additional
“accessory” parts like the
outer tissue of this apple
Stern 1991
Pollination syndromes
Co-evolution between angiosperms and their animal pollinators
- animal gets a reward of sugary nectar (energy-rich)
- plant attaches or dusts animal with pollen, which will then be
transferred to the next flower
Termed co-evolution because changes in one partner trigger
compensating changes in the other
- for example:
This flower has a mechanism causing
stamens to arch over and dust the back
of a honeybee with pollen
Plants pollinated by nocturnal animals
(moths, bats) have flowers that
bloom at night
Many flowers are distinctively shaped so only
a co-evolved pollinator has the right length
appendage to reach in, get the nectar reward
Hummingbird pollinated flowers are
usually red with long tubes
Some flowers have patterns in ultraviolet part of light spectrum
- invisible to us but clear to insect eyes; can form landing strips
Seed dispersal
wind-dispersed
seeds are fluffy
or have “wings”
to increase drag
Fruit dispersal
burrs = dry fruit with hooks to stick to
animals
Fruit dispersal
Most plants invest lots of energy in their
fruit for one reason:

This disperses the offspring of the plant,
as the animal eventually poops out the
undigested seeds somewhere else
The seeds of many plants cannot
develop until they have passed through
an animal’s digestive system!

p. 648 of Freeman 3rd ed.
vascular plants
Gymnosperms
Carnivorous plants
A source of nitrogen is essential for cells to make proteins
- usually nitrate, the water-soluble compound NO3-2
Plants that live in nutrient-poor, swampy
conditions may be unable to get nitrogen
from the soil through their roots
Some therefore capture and digest insects
as a source of nitrogen
Venus flytrap swings closed when 2 of 3
trigger hairs are bent by an insect
Other plants drown insects in contained water
or catch them on sticky leaves
Parasitic angiosperms
Cuscuta sp. (dodder)
Monotropa sp.
Non-photosynthetic; parasitize other plants to obtain nutrition
Plant Chemistry
Because plants can’t move, many produce toxic chemicals to
protect themselves from herbivorous animals and competitors
- many plants leach chemicals out into the surrounding soil to
inhibit growth of competitors (termed allelopathy)
- others produce toxins such as caffeine & nicotine,
to deter herbivorous animals from eating their leaves
Humans use plant chemicals as medicinal or recreational drugs
- 25% of modern medicines involve the plant products
- co-evolved insect herbivores can tolerate chemical defenses
of their particular “host” plant, leading to host specialization
Plant Revenge
Plants can tell when a
caterpillar is eating them,
by recognizing its spit
Plants may release
airborne chemicals that
attract wasps, which come
and sting the caterpillar
The wasps paralyze the
caterpillar and lay their
eggs inside it
 wasp larvae eat the
living but paralyzed
caterpillar from the inside
Plant-insect Coevolution = Biodiversity
Most species on earth, by the numbers, are herbivorous insects
- more than 135,000 species of beetles feed on flowering plants
Studies suggest that when angiosperms started speciating, beetles
that fed on them also divided into specialist populations, which
each evolved into new beetle species
Coevolution can promote species formation
- when one plant evolves into two different species, so do its
parasites, predators and pollinators!
Plant-insect Coevolution = Biodiversity
Consider what happens when an ancestral plant undergoes
speciation and evolves into two distinct plant species...
mountains
Plant-insect Coevolution = Biodiversity
Consider what happens when an ancestral plant undergoes
speciation and evolves into two distinct plant species...
Rain
forest
species
Desert
species
Plant-insect Coevolution = Biodiversity
But what happens to the pollinators (say, butterflies) and herbivores
(beetles) that were symbionts of that ancestral plant...?
pollinator
(butterfly)
herbivore
(beetle)
Plant-insect Coevolution = Biodiversity
But what happens to the pollinators (say, butterflies) and herbivores
(beetles) that were symbionts of that ancestral plant...?
Rain
forest
species
Desert
species
Pollinators and herbivores also form new species when their host plant
speciates
coevolution promotes formation of many new species
Human Dependency on Angiosperms
Crucial to the global carbon cycle
Critical habitat for animals (including us)
Our economy is dependent upon angiosperms (ecosystem
functions)
Sources of everyday products (e.g. hardwoods, medicines)
Source of our food (directly or indirectly)
– over 80% of our food comes from only six species:
rice, soy, wheat, corn, sorghum, and millet