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Plant Evolution Chapter 21 The Plant Kingdom Nearly all are multicelled Vast majority are photoautotrophs Energy from sun Carbon dioxide from air Minerals dissolved in water Setting the Stage for Plants Earth’s atmosphere was originally oxygen free

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plant evolution

Plant Evolution

Chapter 21

the plant kingdom
The Plant Kingdom
  • Nearly all are multicelled
  • Vast majority are photoautotrophs
    • Energy from sun
    • Carbon dioxide from air
    • Minerals dissolved in water
setting the stage for plants
Setting the Stage for Plants
  • Earth’s atmosphere was originally oxygen free
  • Ultraviolet radiation bombarded the surface
  • Photosynthetic cells produced oxygen and allowed formation of a protective ozone layer
invading the land
Invading the Land
  • Cyanobacteria were probably the first to spread into and up freshwater streams
  • Later, green algae and fungi made the journey together
  • Every plant is descended from species of green algae
adaptations to land
Adaptations to Land
  • Root systems
  • Shoot systems
  • Vascular tissues
  • Waxy cuticle for water conservation
evolutionary trend in plant life cycles
Evolutionary Trend in Plant Life Cycles
  • Algae and bryophytes put most energy into making gametophytes
  • Land plants put energy into structures that produce spores and retain, nourish, and protect gametes
milestones in plant evolution
Milestones in Plant Evolution

charophytes

bryophytes

lycophytes

horsetails ferns

cycads

ginkgos

conifers

gnetophytes

flowering plants

seed plants

plants with true leaves

vascular plants

land plants

(closely related groups)

pollen
Pollen
  • Pollen grains are sperm-bearing male gametophytes that develop from microspores
  • Allows transfer of sperm to egg without water
  • Can drift on air currents, or be carried by pollinators
seeds
Seeds
  • Ovules are female reproductive structures that become seeds
  • Consist of:
    • Female gametophyte with egg cell
    • Nutrient-rich tissue
    • Jacket of cell layers that will form seed coat
nonvascular plants
Nonvascular Plants
  • Bryophytes
  • Include 24,000 species of:

Liverworts

Hornworts

Mosses

bryophytes
Bryophytes
  • Small, nonvascular, nonwooody
  • Gametophyte dominates life cycle; has leaflike, stemlike, and rootlike parts
  • Usually live in wet habitats
  • Flagellated sperm require water to reach eggs
moss life cycle
Moss Life Cycle

Development of mature sporophyte (still attached to gametophyte)

Zygote

Diploid Stage

Fertilization

Meiosis

Haploid Stage

Spores released

male

gametophyte

tip

Sperm

Male gametophyte

female

gametophyte

tip

Female gametophyte

Egg

peat mosses
Peat Mosses
  • 350 species
  • Sphagnum is an example
  • Grow in acidic bogs; important ecosystems of cold and temperate regions
  • Peat can be harvested and burned as fuel
marchantia a liverwort
Marchantia: A Liverwort
  • Reproduces asexually by way of gemmae cups
  • Sexual reproduction
      • Gametophytes are male or female
      • Gametes are produced on elevated structures
vascular plants
Vascular Plants
  • Majority of plants
  • Have internal tissues that carry water and solutes
  • Two groups
    • Seedless vascular plants
    • Seed-bearing vascular plants
seedless vascular plants
Seedless Vascular Plants
  • Arose during the Devonian
  • Produce spores but no seeds
  • Main groups:

Lycophytes

Horsetails

Ferns

seedless vascular plants18
Seedless Vascular Plants
  • Like bryophytes:
    • Live in wet, humid places
    • Require water for fertilization
  • Unlike bryophytes:
    • Sporophyte is free-living and has vascular tissues
lycophytes and horsetails
Lycophytes and Horsetails
  • Tree-sized lycophytes lived in Carboniferous swamp forests – 1,100 modern forms are smaller and include club mosses
  • Also as tall as trees, sphenophytes grew in Carboniferous swamp forests – 30 smaller species exist today, known as the “horsetails”
ferns
Ferns
  • 12,000 species, mostly tropical
  • Most common sporophyte structure
    • Perennial underground stem (rhizome)
    • Roots and fronds arise from rhizome
    • Young fronds are coiled “fiddleheads”
    • Mature fronds divided into leaflets
    • Spores form on lower surface of some fronds
fern life cycle
Fern Life Cycle

The sporophyte (still attached to the gametophyte) grows, develops

Sori

rhizome

zygote

Diploid Stage

fertilization

meiosis

Haploid Stage

Spores are released

Spores develop

egg-producing structure

mature gametophyte (underside)

egg

sperm-producing structure

sperm

Spore germinates

gametophyte

ancient carbon treasures
Ancient Carbon Treasures
  • 300 mya – during Carboniferous
  • Mild climate and swamp forests
  • Plants with lignin-reinforced tissues and well-developed root and shoot systems had competitive edge
  • Rising and falling sea levels led to submerged and compressed forests – the source of coal
rise of seed bearing plants
Rise of Seed-Bearing Plants
  • Seeds appeared about 360 million years ago
  • Seed ferns and gymnosperms were dominant at first
  • Angiosperms arose later
seed bearing vascular plants
Seed-Bearing Vascular Plants
  • Gymnosperms arose first
    • Cycads
    • Ginkgos
    • Gnetophytes
    • Conifers
  • Angiosperms arose later
    • Monocots
    • Dicots
seed bearing plants
Seed-Bearing Plants
  • Microspores that give rise to pollen grains
  • Megaspores inside ovules
  • More water-conserving than seedless vascular plants
special traits of seed bearing plants
Special Traits of Seed-Bearing Plants
  • Pollen grains
    • Arise from megaspores
    • Develop into male gametophytes
    • Can be transported without water
  • Seeds
    • Embryo sporophyte inside nutritive tissues and a protective coat
    • Can withstand hostile conditions
gymnosperms
Gymnosperms
  • Plants with “naked seeds”
  • Seeds don’t form inside an ovary
  • Four groups

Conifers Ginkgos

Cycads Gnetophytes

conifer characteristics
Conifer Characteristics
  • Widest known, largest number of living species
  • Woody trees or shrubs
  • Most are evergreen
  • Bear seeds on exposed cone scales
  • Most produce woody cones
conifer distribution
Conifer Distribution
  • Conifers dominated during Mesozoic
  • Reproduce more slowly than angiosperms; at competitive disadvantage in many habitats
  • Still dominate in far North, at higher elevations, and in certain parts of Southern Hemisphere
cycads
Cycads
  • Most diverse during age of dinosaurs
  • Only 130 living species
  • Two species of Zamia are native to U.S.
  • Palmlike appearance
  • Pollen-bearing and seed-bearing cones on different plants
ginkgos
Ginkgos
  • Diverse during age of dinosaurs
  • Only surviving species, Ginkgo biloba, is native to China
  • Deciduous tree with fan-shaped leaves
  • Trees are male or female
  • Female trees produce seeds covered with a fleshy, foul-smelling coat
3 genera of gnetophytes
3 Genera of Gnetophytes
  • Gnetum (tropical climbing vines)
  • Ephedra (joint fir, Mormon tea)
  • Welwitschia mirabilis
pine cones
Pine Cones
  • Woody scales of a “pine cone” are the parts of where megaspores formed and developed into female gametophytes
  • Male cones, where microspores and pollen are produced, are not woody
pine life cycle
PineLifeCycle

Female cone

Sporophyte

Ovule

Male cone

Pollen sac

Seed

Fertilization

Meiosis

Egg

View inside

ovule

Microspores

Megaspores

Pollen tube

angiosperms
Angiosperms
  • Flowering plants
  • Dominant land plants (260,000 species)
  • Defining feature: Ovules and (after fertilization) seeds are enclosed in an ovary
  • Two classes: Monocots and dicots
double fertilization
Double Fertilization
  • Distinctive feature of angiosperms
  • Male gametocyte delivers two sperm to an ovule
  • One fertilizes egg; other fertilizes a cell that gives rise to endosperm that supports embryo
flowering plant life cycle
Flowering Plant Life Cycle

Diploid

Double fertilization

Meiosis

Meiosis

Haploid

Mitosis without cytoplasmic division

Microspores

Pollination

Two sperm enter ovule

Female gametophyte

flowering plant diversity
Flowering Plant Diversity
  • Almost 90 percent of living plants are angiosperms
  • Three major groups:
    • Magnoliids – 9,200 species, such as pepper plants
    • Eudicots – 170,000 species, including daisies
    • Monocots – 80,000 species, including grasses
flowering plant evolution
Flowering Plant Evolution

water lilies

star anise

Amborella

eudicots

magnoliids

monocots

basal groups

deforestation
Deforestation
  • Result of demand for wood as fuel and lumber; cultivation of land for agriculture
  • Greatest occurrence in Brazil, Indonesia, Columbia, and Mexico