plant

1. An overview of PlantAn overview of Plant
EvolutionEvolution
Key Moments in the life of KingdomKey Moments in the life of Kingdom
PlantaePlantae
By Dr. Neil BuckleyBy Dr. Neil Buckley
Buckley, N. (n.d.). Plattsburgh State Faculty and ResearchBuckley, N. (n.d.). Plattsburgh State Faculty and Research
Web Sites. Retrieved May 21, 2015, fromWeb Sites. Retrieved May 21, 2015, from
http://faculty.plattsburgh.edu/http://faculty.plattsburgh.edu/

2. How did we get from here to there?How did we get from here to there?

3. Key “Moments” in PlantKey “Moments” in Plant
EvolutionEvolution
• The Transition to LandThe Transition to Land
• Development of Vascular SystemsDevelopment of Vascular Systems
• Evolution of HeterosporyEvolution of Heterospory
• Evolution of the SeedEvolution of the Seed
• Diversification of the AngiospermsDiversification of the Angiosperms

4.  The risks: Harsh environment…The risks: Harsh environment…

Heat, dessication, damage by UV raysHeat, dessication, damage by UV rays
 The rewards: Great opportunity…The rewards: Great opportunity…
 Plentiful COPlentiful CO22, sunlight, few competitors or, sunlight, few competitors or
herbivores.herbivores.

The importance: paved the way for otherThe importance: paved the way for other
organismsorganisms
Food for herbivores; First soils!Food for herbivores; First soils!
1. The transition to Land -1. The transition to Land - ca. 475 myaca. 475 mya

5. Ancestors of the PlantaeAncestors of the Plantae
 The Plantae evolved from green algae, mostThe Plantae evolved from green algae, most
likely a group called the charophytes.likely a group called the charophytes.
 Evidence:Evidence:

Plants and green algae contain chlorophyll b.Plants and green algae contain chlorophyll b.

Chloroplasts of both have a similar structure in whichChloroplasts of both have a similar structure in which
thylakoid membranes are stacked as grana.thylakoid membranes are stacked as grana.

Cell wall structure of both is very similar (about 22-Cell wall structure of both is very similar (about 22-
26% cellulose)26% cellulose)

DNA sequence data supports close relationshipDNA sequence data supports close relationship
between these groups.between these groups.

8. Challenges of living on landChallenges of living on land
 Water is a supportive medium, air is not.Water is a supportive medium, air is not.
 Algae are surrounded by a medium thatAlgae are surrounded by a medium that
contains water and minerals and can takecontains water and minerals and can take
in their requirements across the wholein their requirements across the whole
body.body.

9. Challenges of living on landChallenges of living on land
 To survive on land a plant must:To survive on land a plant must:

Avoid drying out.Avoid drying out.

Be able to hold itself up.Be able to hold itself up.

Possess differentiated tissues because airPossess differentiated tissues because air
and soil differ in composition and resources.and soil differ in composition and resources.
Exploiting these different media requiresExploiting these different media requires
specialized tissues.specialized tissues.

Solve the problem of reproducing outsideSolve the problem of reproducing outside
water.water.

10. Transition to landTransition to land
 It is believed that ancestral charophytes lived inIt is believed that ancestral charophytes lived in
shallow water that sometimes dried out (as doshallow water that sometimes dried out (as do
modern charophytes).modern charophytes).
 Selection would have favored adaptations inSelection would have favored adaptations in
these charophytes to resist drying out such asthese charophytes to resist drying out such as
waxy cuticles and protecting developingwaxy cuticles and protecting developing
embryos within layers of tissue. Theseembryos within layers of tissue. These
preadaptationspreadaptations facilitated the transition ontofacilitated the transition onto
land.land.

11. Reproduction on landReproduction on land
 Moving onto land required theMoving onto land required the
development of new forms ofdevelopment of new forms of
reproduction.reproduction.
 Algae shed their gametes into the water,Algae shed their gametes into the water,
but on land gametes must be protectedbut on land gametes must be protected
against desiccation.against desiccation.

12. Reproduction on landReproduction on land
 Plants produce gametes withinPlants produce gametes within
gametangia (protective layers of tissuegametangia (protective layers of tissue
that prevent gametes from drying out).that prevent gametes from drying out).
 Egg is fertilized within femaleEgg is fertilized within female
gametangium (called the archegonium)gametangium (called the archegonium)
and embryo develops for some time insideand embryo develops for some time inside
archegonium.archegonium.

14. EmbryophytesEmbryophytes
 Retention of the developing embryo byRetention of the developing embryo by
plants is a fundamental difference fromplants is a fundamental difference from
algae. Because this difference is so basic,algae. Because this difference is so basic,
plants are sometimes described asplants are sometimes described as
embryophytes.embryophytes.

15. Transition to landTransition to land
 The ancestor of modern plants onceThe ancestor of modern plants once
established on land had enormousestablished on land had enormous
opportunities.opportunities.
 No competition for sunlight or mineralsNo competition for sunlight or minerals
and no herbivores.and no herbivores.
 Selection rapidly led to a massiveSelection rapidly led to a massive
diversification of plants.diversification of plants.

16. 2. Rise of Vascular plants2. Rise of Vascular plants
 The first land plants lacked vascular tissueThe first land plants lacked vascular tissue
(as is true of most mosses today) so they(as is true of most mosses today) so they
could not transport water, sugars orcould not transport water, sugars or
minerals around the plant.minerals around the plant.
 Lack of vascular tissue also, of course,Lack of vascular tissue also, of course,
limited the size of plants.limited the size of plants.

17. 2. Rise of Vascular plants2. Rise of Vascular plants
 Once the first plants moved onto land, selectionOnce the first plants moved onto land, selection
quickly led to the development of specializedquickly led to the development of specialized
roots and shoots.roots and shoots.
 Roots and shoots required the development of aRoots and shoots required the development of a
vascular system to move water and othervascular system to move water and other
essentials around the plant and by aboutessentials around the plant and by about
400mya early vascular plants had begun to400mya early vascular plants had begun to
diversify.diversify.
 Large ferns and otherLarge ferns and other seedless plantsseedless plants came tocame to
dominate the land in the Carboniferous Period.dominate the land in the Carboniferous Period.

18. 3. Transition from homospory to
heterospory
 Homospory means spores are the sameHomospory means spores are the same
size and heterospory that microsporessize and heterospory that microspores
(male) and megaspores (female) differ in(male) and megaspores (female) differ in
size.size.
 Microspores develop into maleMicrospores develop into male
gametophytes and megaspores intogametophytes and megaspores into
female gametophytes.female gametophytes.

19. 3. Transition from homospory to
heterospory
 Mosses and most ferns are homosporous.Mosses and most ferns are homosporous.
Conifers and flowering plants are heterosporous.Conifers and flowering plants are heterosporous.
 Homosporous plants produce spores thatHomosporous plants produce spores that
develop into bisexual gametophytes thatdevelop into bisexual gametophytes that
produce both sperm and eggs.produce both sperm and eggs.
 For successful fertilization, homosporous plantsFor successful fertilization, homosporous plants
need water in the form of rainfall when gametesneed water in the form of rainfall when gametes
are mature.are mature.

20. 3. Transition from homospory to
heterospory
 Some homosporous plants evolvedSome homosporous plants evolved
heterospory.heterospory.
 With heterospory in which the femaleWith heterospory in which the female
gametophyte is enclosed and protectedgametophyte is enclosed and protected
and there is no need for water to ensureand there is no need for water to ensure
fertilization.fertilization.
 Heterospory led to the evolution of seeds.Heterospory led to the evolution of seeds.

21. 4. Evolution of the seed4. Evolution of the seed
 In mosses the life cycle is dominated by theIn mosses the life cycle is dominated by the
gametophyte generation.gametophyte generation.
 In ferns the sporophyte generation is dominantIn ferns the sporophyte generation is dominant
and the gametophyte is reduced, but still visibleand the gametophyte is reduced, but still visible
to the naked eye.to the naked eye.
 In seed plants the gametophyte generation is soIn seed plants the gametophyte generation is so
reduced that in most cases it is microscopicreduced that in most cases it is microscopic

22. AlternationAlternation
ofof
GenerationsGenerations

24. 4. Evolution of the seed4. Evolution of the seed
 The reduction of size of the femaleThe reduction of size of the female
gametophyte has meant that it can begametophyte has meant that it can be
enclosed and protected within sporophyteenclosed and protected within sporophyte
tissue (the ovule).tissue (the ovule).
 The female gametophyte is not dispersedThe female gametophyte is not dispersed
and is protected from drying out and otherand is protected from drying out and other
hazards.hazards.

25. 4. Evolution of the seed4. Evolution of the seed
 The male gametophyte is what isThe male gametophyte is what is
dispersed in seed plants. It is alsodispersed in seed plants. It is also
protected by sporophyte tissue, the pollenprotected by sporophyte tissue, the pollen
grain.grain.
 Pollen lands on the ovule and eventuallyPollen lands on the ovule and eventually
fertilizes egg produced by the femalefertilizes egg produced by the female
gametophyte. Embryo (sporophyte 2n)gametophyte. Embryo (sporophyte 2n)
then develops.then develops.

27. Advantages of seedsAdvantages of seeds
 Provides protection and nourishment forProvides protection and nourishment for
developing embryo.developing embryo.
 Dispersal: seeds can be dispersed moreDispersal: seeds can be dispersed more
widely than spores by enclosing them in awidely than spores by enclosing them in a
bribe (fruit) and having animals movebribe (fruit) and having animals move
them.them.
 Dormancy: the developing embryo isDormancy: the developing embryo is
protected and can wait a long time toprotected and can wait a long time to
germinate when conditions are good.germinate when conditions are good.

29. Seeds vs sporesSeeds vs spores
 Seeds are better than spores becauseSeeds are better than spores because
spores have a short lifetime.spores have a short lifetime.
 Spores are thinner walled and moreSpores are thinner walled and more
vulnerable to pathogens and damage.vulnerable to pathogens and damage.

30. Angiosperm diversificationAngiosperm diversification
 The angiosperms have been enormouslyThe angiosperms have been enormously
successful.successful.
 There are now about 235,000 species inThere are now about 235,000 species in
comparison to just over 700comparison to just over 700
gymnosperms.gymnosperms.

31. Flowers and fruitFlowers and fruit
 The key to the success of theThe key to the success of the
Angiosperms has been that they haveAngiosperms has been that they have
evolved flowers and fruit.evolved flowers and fruit.
 Fruit protects the seeds and aids in theirFruit protects the seeds and aids in their
dispersal.dispersal.
 The fruit is a bribe. Animals eat the fruitThe fruit is a bribe. Animals eat the fruit
and spread the seeds.and spread the seeds.

33. Flowers and pollinationFlowers and pollination
 A major advantage of flowers is that they haveA major advantage of flowers is that they have
allowed angiosperms to use other organisms toallowed angiosperms to use other organisms to
move their pollen about.move their pollen about.
 Bees, bats, birds and others all transport pollen.Bees, bats, birds and others all transport pollen.
They are attracted to flowers by the nectar andThey are attracted to flowers by the nectar and
pollen [bribes] provided by the plant and whenpollen [bribes] provided by the plant and when
they visit multiple flowers they move pollen fromthey visit multiple flowers they move pollen from
one to the nextone to the next