1. The Greening of Earth
For more than the first 3 billion years of Earth’s history, the terrestrial surface was lifeless
Cyanobacteria likely existed on land 1.2 billion years ago
Around 500 million years ago, small plants, fungi, and animals emerged on land

2. Since colonizing land, plants have diversified into roughly 290,000 living species
Land plants are defined as having terrestrial ancestors, even though some are now aquatic
Plants supply oxygen and are the ultimate source of most food eaten by land animals
though diatoms are thought to provide ~35% of the world’s oxygen!

3. Land plants evolved from green algae
Green algae called charophytes are the closest relatives of land plants

6. Comparisons of both nuclear and chloroplast genes point to charophytes as the closest living relatives of land plants
Note that land plants are not descended from modern charophytes, but share a common ancestor with modern charophytes

7. Adaptations Enabling the Move to Land
In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out
obviously important in allowing movement out of water!
Sporopollenin is also found in plant spore walls
The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful CO2, nutrient-rich soil, and few herbivores or pathogens
Land presented challenges: a scarcity of water and lack of structural support

8. Defining Plants

9. 1 m Figure 29.7 1 Origin of land plants (about 475 mya) 2
Origin of vascular plants (about 425 mya) 3
Origin of extant seed plants (about 305 mya)
Liverworts
Nonvascular plants (bryophytes)
ANCESTRAL GREEN ALGA
Land plants 1
Mosses
Hornworts
Lycophytes (club mosses, spike mosses, quillworts)
Seedless vascular plants 2
Pterophytes (ferns, horsetails, whisk ferns)
Vascular plants
Figure 29.7 Highlights of plant evolution.
Gymnosperms 3
Seed plants
Angiosperms
500
450
400
350
300 50
Millions of years ago (mya)
1 m

10. Defining Plants
Embryophytes

11. The diploid embryo is retained within the tissue of the female gametophyte
Nutrients are transferred from parent to embryo through placental transfer cells
Land plants are called embryophytes because of the dependency of the embryo on the parent

12. Defining Plants Land plants have three major derived traits:
Multicellular haploid and diploid phases
Embryos are dependent on protection and nutrition from parental tissue (embryophyte)
Apical meristems – areas of undifferentiated active cell division at the tips of roots and branches.

13. 1 m Embryo Maternal tissue 10 m Figure 29.5ba
Figure 29.5 Exploring: Derived Traits of Land Plants
10 m
1 m

14. Apical meristematic tissue that develop into roots and shoots.

15. Land plants can be informally grouped based on the presence or absence of vascular tissue
Most plants have vascular tissue; these constitute the vascular plants
Nonvascular plants are commonly called bryophytes
Bryophytes are not a monophyletic group; their relationships to each other and to vascular plants is unresolved

16. Defining Plants
Vascular Plants

17. A seed is an embryo and nutrients surrounded by a protective coat
Seed plants form a clade and can be divided into further clades
Gymnosperms, the “naked seed” plants, including the conifers
Angiosperms, the flowering plants

18. Defining Plants
Seed Plants

19. Table 29.1 Ten Phyla of Extant Plants
1 m

20. Evolutionary adaptations
Evolution of leaves
Increased photosynthetic surface area.
Stomata (vascular plants) for gas exchange.
Waxy cuticle to prevent water loss.
diversification of leaf structure

21. Plant Life Cycles Humans have a diplontic life cycle
-Only the diploid stage is multicellular
Plants have a haplodiplontic life cycle
-Multicellular diploid stage = Sporophyte (2n)
(the familiar plant body)
-Multicellular haploid stage = Gametophyte (n)
(the pollen and the embryo sac)

22. Alternation of generations - gametophyte and sporophyte are both represented.
Gametophyte is the dominant generation in mosses and ferns.
Sporophyte is the dominant generation in higher plants.

24. Plant Life Cycles Sporophyte produces haploid spores by meiosis
Spores divide mitotically, producing the gametophyte
Gametophyte produces
gametes by mitosis
Gametes fuse to form
the diploid sporophyte

25. Fern

26. Plant Life Cycles As more complex plants evolved…
1. Diploid stage became the dominant portion of the life cycle (seed plants).
2. Gametophyte became more limited in size.
3. Sporophyte became nutritionally independent.

27. Evolutionary adaptations
Vascular plants evolved..
Xylem for water and mineral conduction (except bryophytes)
Phloem for nutrient conduction (except bryophytes)

28. Plant Polyploidy Evolutionary adaptation? Is it beneficial? Why?
Comai, L. THE ADVANTAGES AND DISADVANTAGES OF BEING POLYPLOID. Nature 2005.
Ploidy
# of chromosomes
Characteristics
Diploid 14
Its fruit has a poor flavor, and it is of no commercial value.
It has extremely small berries, fine flavor, surprisingly little of the usual strawberry aroma, but a refreshing acidity. They sometimes ripen without becoming red.
Hexaploid 42
Also known as the musk strawberry. Its French name "hautbois" strawberry is anglicized as "hautboy" strawberry.
Octoploid 56
The "common strawberry." The fruit is widely appreciated, has a characteristic aroma, bright red color, and juicy texture. It is consumed in large quantities.
Also known as the beach strawberry, Chilean strawberry, or coastal strawberry.
It has relatively large berries for a wild species, which are similar in appearance to those of Fragaria virginiana.
This species is also sometimes called "Wild Strawberry" or "Common Strawberry".
Decaploid 70
This species is not yet commercially important, but it remains under development. Its berries are flavorful but small.

29. Bryophytes Bryophytes are the basal land plant clade.
Bryophytes are also called the nonvascular plants.

31. Bryophytes
Bryophytes lack xylem and phloem (specialized transport cells).
Simple, but highly adapted to diverse terrestrial environments.
Gametophyte is dominant stage.

32. Bryophytes Liverworts (phylum Hepaticophyta)
- Have flattened gametophytes with liver-like lobes.
- Also undergo asexual reproduction
-No stomata

33. Bryophytes Hornworts (phylum Anthocerotophyta) -Sporophyte has stomata
-Sporophyte is photosynthetic
-Cells have a single large chloroplast

34. Bryophytes Mosses (phylum Bryophyta)
-Gametophytes consist of small, leaflike structures around a stemlike axis
-Anchored to substrate by rhizoids
-Multicellular gametangia form at the tips of gametophytes
-Archegonia – Female gametangia
-Antheridia – Male gametangia
Mosses withstand drought, but not air pollution

36. Tracheophytes

37. Features of Tracheophyte Plants
Cooksonia, the first vascular land plant, appeared about 425 MYA.
-Only a few centimeters tall
-No roots or leaves
-Homosporous

38. Features of Tracheophyte Plants
They have a branched sporophyte that is independent of the gametophyte.

39. Features of Tracheophyte Plants
Vascular tissues are of two types
-Xylem – Conducts water and dissolved minerals upward from the roots
-Phloem – Conducts sugar and hormones throughout the plant
-These enable enhanced height and size in the tracheophytes
Tracheophytes are also characterized by the presence of a cuticle and stomata.

40. Features of Tracheophyte Plants
Vascular plants have gametophytes reduced in size and complexity relative to sporophytes
Seeds
-Highly-resistant structures that protect the plant embryo
Fruits in flowering plants add a layer of protection to seeds
-Also attract animals that disperse seeds

41. Tracheophyte Plants
Vascular plants include seven extant phyla grouped in three clades.
1. Lycophytes (club mosses)
2. Pterophytes (ferns and their relatives)
3. Seed plants (Gymnosperms and Angiosperms)

42. Lycophytes Club mosses are the earliest vascular plants.
-They lack seeds

43. Lycophytes
Homosporous (club mosses) or heterosporous (spike mosses and quillworts).

44. Pterophytes
The phylogenetic relationship among ferns and their relatives is still being sorted out

45. Pterophytes
Ferns
-The most abundant group of seedless vascular plants with about 12,000 species
-The conspicuous sporophyte and much smaller gametophyte are both photosynthetic

46. Pterophytes Fern reproduction
-Most ferns (and other Pterophytes) are homosporous
-Produce distinctive sporangia in clusters called sori on the back of the fronds

47. Fern life cycle

48. The Evolution of Seed Plants
Seed plants first appeared MYA
-Evolved from spore-bearing plants known as progymnosperms
The seed represents an important advance
1. Protects the embryo
2. Easily dispersed
3. Introduces a dormant phase in the life cycle

49. The Evolution of Seed Plants
Besides seeds, seed plants have…
Reduced gametophytes
Heterospory
Ovules
Pollen

50. Ferns and other seedless
Figure 30.2
PLANT GROUP
Mosses and other
nonvascular plants
Ferns and other seedless
vascular plants
Seed plants (gymnosperms and angiosperms)
Reduced, independent
(photosynthetic and
free-living)
Reduced (usually microscopic), dependent on surrounding
sporophyte tissue for nutrition
Gametophyte
Dominant
Reduced, dependent on
gametophyte for nutrition
Sporophyte
Dominant
Dominant
Gymnosperm
Angiosperm
Sporophyte
(2n)
Microscopic female
gametophytes (n) inside
ovulate cone
Sporophyte
(2n)
Microscopic
female
gametophytes
(n) inside
these parts
of flowers
Gametophyte
(n)
Example
Figure 30.2 Gametophyte-sporophyte relationships in different plant groups.
Microscopic
male
gametophytes
(n) inside
these parts
of flowers
Microscopic male
gametophytes (n)
inside pollen
cone
Sporophyte (2n)
Sporophyte (2n)
Gametophyte
(n) 50

51. The Evolution of Seed Plants
Seed plants produce 2 kinds of gametophytes
-Male gametophytes
-Pollen grains
-Dispersed by wind or a pollinator
-Female gametophytes
-Develop within an ovule
-Enclosed within diploid sporophyte tissue

52. Ovule = megasporangium + megaspore + integument

53. Pollen = coat + pollen grain
Embryo = pollinated ovule
Seed = embryo, food supply and protective coat

54. Seed plants
Gymnosperms – “naked seeds” – seeds are not enclosed in ovaries, usually on sporophylls forming cones (strobili)
Angiosperms – enclosed in mature ovaries (aka fruit).

55. Gymnosperms There are four living groups: Coniferophytes Cycadophytes
Gnetophytes
Ginkgophytes
All lack flowers and fruits.

56. Gymnosperms
Conifers (phylum Coniferophyta) are the largest gymnosperm phylum.
Include:
-Pines, spruces, firs, cedars and others
-Coastal redwood – Tallest tree
-Bristlecone pine – Oldest living tree

57. Gymnosperms
Conifers (phylum Coniferophyta) are sources of important products:
-Timber, paper, resin and taxol (anti-cancer)

58. Gymnosperms -More than 100 species, all in the Northern hemisphere
Pines
-More than 100 species, all in the Northern hemisphere
-Produce tough needlelike leaves in clusters
-Leaves have:
1. Thick cuticle and recessed stomata
2. Canals into which cells secrete resin

59. Gymnosperms Pine reproduction
-Male gametophytes (pollen grains) develop from microspores in male cones by meiosis
-Female pine cones form on the upper branches of the same tree
-Female cones are larger, and have woody scales
-Two ovules develop on each scale

60. Gymnosperms Pine reproduction
-Each ovule contains a megasporangium called the nucellus
-Surrounded by the integument
-Opening – Micropyle
-One layer becomes the seed coat
-While scales of female cone are open, pollen grains drift down between them
-Are drawn to top of nucellus

61. Gymnosperms Pine reproduction
-While female gametophyte is developing, a pollen tube emerges from the pollen grain
-It digests its way to the archegonium
-Fifteen months after pollination, pollen tube reaches archegonium and delivers its sperm

66. Angiosperms Angiosperms are the flowering plants
-Ovules are enclosed in diploid tissue at the time of pollination
-The carpel, a modified leaf that covers seeds, develops into fruit

67. Angiosperms

68. Angiosperms

69. Angiosperms Flower morphology
-Primordium develops into a bud at the end of a stalk called the pedicel
-Pedicel expands at the tip to form a receptacle, to which other parts attach
-Flower parts are organized in circles called whorls

70. Angiosperms Flower morphology -Outermost whorl = Sepals
-Second whorl = Petals
-Third whorl = Stamens (androecium)
-Each stamen has a pollen-bearing anther and a filament (stalk)
-Innermost whorl = Gynoecium
-Consists of one or more carpels that house the female gametophyte

71. Angiosperms

72. Angiosperms Carpel structure -Three major regions
-Ovary = Swollen base containing ovules
-Later develops into a fruit
-Stigma = Tip
-Style = Neck or stalk

73. Angiosperm Life Cycle Pollen production occurs in the anthers
-It is similar but less complex than female gametophyte formation
-Diploid microspore mother cells undergo meiosis to produce four haploid microspores
-Binucleate microspores become pollen grains

74. Angiosperm Life Cycle
Pollination is the mechanical transfer of pollen from anther to stigma
-Pollen grains develop a pollen tube that is guided to the embryo sac
-One of the two pollen grain cells lags behind
-This generative cell divides to produce two sperm cells

75. Angiosperm Life Cycle
As the pollen tube enters the embryo sac, a double fertilization occurs
-One sperm unites with egg to form the diploid zygote
-Other sperm unites with the two polar nuclei to form the triploid endosperm
-Provides nutrients to embryo
When the seed germinates, a young sporophyte plant emerges

77. Angiosperm Life Cycle Angiosperms include:
-Eudicots (about 175,000 species)
-Trees, shrubs, snapdragons, peas, other
-Use flowers to attract insect pollinators
-Monocots (about 65,000 species)
-Grasses, lilies, palms, irises, others
-Some rely on wind for pollination
Note: Self-pollination may also occur