- Plants and fungi were early colonizers of land, with fungi potentially colonizing before plants. They formed symbiotic partnerships through mycorrhizal relationships that helped plants obtain nutrients. - Key adaptations like a waxy cuticle, specialized tissues for water transport, and stomata allowed early land plants to survive out of water. Fossil evidence shows simple plant structures existed over 400 million years ago. - Fungi play an essential role in nutrient cycling and decomposition on land through their mycelial networks and ability to secrete digestive enzymes to absorb nutrients. Mycorrhizal relationships with plant roots are mutually beneficial.

1. CAMPBELL BIOLOGY IN FOCUS
© 2014 Pearson Education, Inc.
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
26
The Colonization
of Land by Plants
and Fungi

2. © 2014 Pearson Education, Inc.
Overview: The Greening of Earth
 For more than the first 2 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
 The first forests formed about 385 million years ago

3. © 2014 Pearson Education, Inc.
Figure 26.1

4. © 2014 Pearson Education, Inc.
 Although not closely related, plants and fungi
colonized the land as partners before animals arrived
 Plants supply oxygen and are the ultimate source of
most food eaten by land animals
 Fungi break down organic material and recycle
nutrients

5. © 2014 Pearson Education, Inc.
Figure 26.2
Charophyte
algae
Fungi
Animals
Plants

6. © 2014 Pearson Education, Inc.
Concept 26.1: Fossils show that plants colonized
land more than 470 million years ago
 Green algae called charophytes are the closest
relatives of land plants

7. © 2014 Pearson Education, Inc.
Evidence of Algal Ancestry
 Many characteristics of land plants also appear in
some algae
 However, land plants share certain distinctive traits
with only charophytes, including
 Rings of cellulose-synthesizing complexes
 Structure of flagellated sperm

8. © 2014 Pearson Education, Inc.
Figure 26.3
30 nm

9. © 2014 Pearson Education, Inc.
 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

10. © 2014 Pearson Education, Inc.
Figure 26.4
40 µm
Coleochaete orbicularis, a
disk-shaped charophyte that
also lives in ponds (LM)
Chara vulgaris, a pond organism

11. © 2014 Pearson Education, Inc.
Figure 26.4a
Chara vulgaris, a pond organism

12. © 2014 Pearson Education, Inc.
Figure 26.4b
40 µm
Coleochaete orbicularis, a disk-
shaped charophyte that also lives
in ponds (LM)

13. © 2014 Pearson Education, Inc.
Adaptations Enabling the Move to Land
 In charophytes, a layer of a durable polymer called
sporopollenin prevents exposed zygotes from
drying out
 Sporopollenin is also found in plant spore walls
 The movement onto land by charophyte ancestors
provided unfiltered sunlight, more plentiful CO2, and
nutrient-rich soil
 Land presented challenges: a scarcity of water and
lack of structural support

14. © 2014 Pearson Education, Inc.
 The accumulation of traits that facilitated survival on
land may have opened the way to its colonization by
plants
 Systematists are currently debating the boundaries
of the plant kingdom
 Until this debate is resolved, we define plants as
embryophytes, plants with embryos
Animation: Moss Life Cycle
Animation: Fern Life Cycle

15. © 2014 Pearson Education, Inc.
Figure 26.5
ANCESTRAL
ALGA
Red algae
Chlorophytes
Plantae
Charophytes
Embryophytes
Viridiplantae
Streptophyta

16. © 2014 Pearson Education, Inc.
Derived Traits of Plants
 Key traits that appear in nearly all land plants but
are absent in the charophytes include
 Alternation of generations
 Multicellular, dependent embryos
 Walled spores produced in sporangia
 Apical meristems

17. © 2014 Pearson Education, Inc.
 Alternation of generations
 The gametophyte is haploid and produces haploid
gametes by mitosis
 Fusion of the gametes gives rise to the diploid
sporophyte, which produces haploid spores by
meiosis

18. © 2014 Pearson Education, Inc.
Figure 26.6
FERTILIZATIONMEIOSIS
Key
Alternation of generations
Mitosis
Gametophyte
(n)
Gamete from
another plant
Wall ingrowths
Mitosis
Spore Gamete
Zygote
MitosisSporophyte
(2n)
Placental transfer
cell (blue outline)
Multicellular, dependent embryos
Embryo
Maternal tissue
Haploid (n)
Diploid (2n)
10 µm
2 µm
2n
n
n
n
n

19. © 2014 Pearson Education, Inc.
Figure 26.6a
FERTILIZATIONMEIOSIS
Key
Alternation of generations
Mitosis
Gametophyte
(n)
Gamete from
another plant
Mitosis
Spore Gamete
Zygote
MitosisSporophyte
(2n)
Haploid (n)
Diploid (2n)
2n
n
n
n
n

20. © 2014 Pearson Education, Inc.
Figure 26.6b
Wall ingrowths
Placental transfer
cell (blue outline)
Multicellular, dependent embryos
Embryo
Maternal tissue
10 µm
2 µm

21. © 2014 Pearson Education, Inc.
Figure 26.6ba
Embryo
Maternal
tissue
10 µm

22. © 2014 Pearson Education, Inc.
Figure 26.6bb
Wall ingrowths
Placental transfer
cell (blue outline)
2 µm

23. © 2014 Pearson Education, Inc.
 Multicellular, dependent embryos
 The multicellular, 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

24. © 2014 Pearson Education, Inc.
 Walled spores produced in sporangia
 Sporangia are multicellular organs that produce
spores
 Spore walls contain sporopollenin, which makes them
resistant to harsh environments

25. © 2014 Pearson Education, Inc.
Figure 26.7
Gametophyte
Sporophyte
Sporangium
Spores
Longitudinal section of
Sphagnum sporangium
(LM)

26. © 2014 Pearson Education, Inc.
Figure 26.7a
Gametophyte
Sporophyte
Sporangium

27. © 2014 Pearson Education, Inc.
Figure 26.7b
Sporangium
Spores
Longitudinal section of
Sphagnum sporangium
(LM)

28. © 2014 Pearson Education, Inc.
 Apical meristems
 Localized regions of cell division at the tips of roots
and shoots are called apical meristems
 Apical meristem cells can divide throughout the
plant’s life

29. © 2014 Pearson Education, Inc.
 Additional derived traits include
 Cuticle, a waxy covering of the epidermis that
functions in preventing water loss and microbial
attack
 Stomata, specialized pores that allow the exchange
of CO2 and O2 between the outside air and the plant

30. © 2014 Pearson Education, Inc.
Early Land Plants
 Fossil evidence indicates that plants were on land at
least 470 million years ago
 Fossilized spores and tissues have been extracted
from 450-million-year-old rocks

31. © 2014 Pearson Education, Inc.
Figure 26.8
(a) Fossilized
spores
(b) Fossilized
sporophyte
tissue

32. © 2014 Pearson Education, Inc.
Figure 26.8a
(a) Fossilized
spores

33. © 2014 Pearson Education, Inc.
Figure 26.8b
(b) Fossilized
sporophyte
tissue

34. © 2014 Pearson Education, Inc.
 Large plant structures, such as the sporangium of
Cooksonia, appeared in the fossil record 425 million
years ago
 By 400 million years ago, a diverse assemblage of
plants lived on land
 Unique traits in these early plants included
specialized tissues for water transport, stomata, and
branched sporophytes
Animation: Fungal Reproduction Nutrition

35. © 2014 Pearson Education, Inc.
Figure 26.UN01
Cooksonia sporangium fossil (425 million
years old)
0.3 mm

36. © 2014 Pearson Education, Inc.
Figure 26.9
Sporangia
Rhizoids
25 µm
2 cm

37. © 2014 Pearson Education, Inc.
Figure 26.9a
25 µm

38. © 2014 Pearson Education, Inc.
Concept 26.2: Fungi played an essential role in
the colonization of land
 Fungi may have colonized land before plants
 Mycorrhizae are symbiotic associations between
fungi and land plants that may have helped plants
without roots to obtain nutrients

39. © 2014 Pearson Education, Inc.
Fungal Nutrition
 Fungi are heterotrophs and absorb nutrients from
outside of their body
 Fungi use enzymes to break down a large variety
of complex molecules into smaller organic
compounds
 Fungi can digest compounds from a wide range of
sources, living or dead

40. © 2014 Pearson Education, Inc.
Adaptations for Feeding by Absorption
 Fungal cell walls contain chitin, a strong but flexible
nitrogen-containing polysaccharide
 The most common body structures are multicellular
filaments and single cells (yeasts)
 Some species grow as either filaments or yeasts;
others grow as both

41. © 2014 Pearson Education, Inc.
 The morphology of multicellular fungi enhances their
ability to absorb nutrients
 Fungi consist of mycelia, networks of branched
hyphae, filiments adapted for absorption
 A mycelium’s structure maximizes its surface-area-
to-volume ratio

42. © 2014 Pearson Education, Inc.
Figure 26.10
Hyphae
Mycelium
60 µm
Reproductive
structure
Spore-producing
structures

43. © 2014 Pearson Education, Inc.
Figure 26.10a

44. © 2014 Pearson Education, Inc.
Figure 26.10b
Mycelium

45. © 2014 Pearson Education, Inc.
Figure 26.10c
60 µm

46. © 2014 Pearson Education, Inc.
Specialized Hyphae in Mycorrhizal Fungi
 Some fungi have specialized hyphae called
haustoria that allow them to extract or exchange
nutrients with plant hosts

47. © 2014 Pearson Education, Inc.
Figure 26.11
Fungal hypha
Haustorium
Plant cell
Plant cell
plasma
membrane
Plant
cell
wall

48. © 2014 Pearson Education, Inc.
 Mycorrhizae are mutually beneficial relationships
between fungi and plant roots
 Ectomycorrhizal fungi form sheaths of hyphae
over a root and also grow into the extracellular
spaces of the root cortex
 Arbuscular mycorrhizal fungi extend hyphae
through the cell walls of root cells and into tubes
formed by invagination of the root cell membrane

49. © 2014 Pearson Education, Inc.
Sexual and Asexual Reproduction
 Fungi propagate themselves by producing vast
numbers of spores, either sexually or asexually
 Fungi can produce spores from different types of life
cycles

50. © 2014 Pearson Education, Inc.
Figure 26.12-1
Key
GERMINATION
Spores
ASEXUAL
REPRODUCTION
Spore-
producing
structures
Mycelium
Haploid (n)
Diploid (2n)
Heterokaryotic

51. © 2014 Pearson Education, Inc.
Figure 26.12-2
Zygote
PLASMOGAMY
Key
KARYOGAMY
GERMINATION
Spores SEXUAL
REPRODUCTION
ASEXUAL
REPRODUCTION
Heterokaryotic
stage
Spore-
producing
structures
Mycelium
Haploid (n)
Diploid (2n)
Heterokaryotic

52. © 2014 Pearson Education, Inc.
Figure 26.12-3
Zygote
Spores
PLASMOGAMY
Key
KARYOGAMY
GERMINATION MEIOSIS
GERMINATION
Spores SEXUAL
REPRODUCTION
ASEXUAL
REPRODUCTION
Heterokaryotic
stage
Spore-
producing
structures
Mycelium
Haploid (n)
Diploid (2n)
Heterokaryotic

53. © 2014 Pearson Education, Inc.
 Plasmogamy is the union of cytoplasm from two
haploid parent mycelia
 Hours, days, or even centuries may pass before the
occurrence of karyogamy, nuclear fusion
 During karyogamy, the haploid nuclei fuse,
producing diploid cells
 The diploid phase is short-lived and undergoes
meiosis, producing haploid spores

54. © 2014 Pearson Education, Inc.
 In addition to sexual reproduction, many fungi can
reproduce asexually
 Molds produce haploid spores by mitosis and form
visible mycelia
 Single-celled yeasts reproduce asexually through
cell division

55. © 2014 Pearson Education, Inc.
The Origin of Fungi
 Fungi and animals are more closely related to each
other than they are to plants or other eukaryotes

56. © 2014 Pearson Education, Inc.
 DNA evidence suggests that
 Fungi are most closely related to unicellular
protists called nucleariids
 Animals are most closely related to unicellular
choanoflagellates
 This suggests that multicellularity arose separately in
animals and fungi
 The oldest undisputed fossils of fungi are only about
460 million years old

57. © 2014 Pearson Education, Inc.
Figure 26.13
50 µm

58. © 2014 Pearson Education, Inc.
The Move to Land
 Fungi were among the earliest colonizers of land and
probably formed mutualistic relationships with early
land plants
 For example, 405-million-year-old fossils of
Aglaophyton contain evidence of fossil hyphae
penetrating plant cells
Video: Phlyctochytrium Spores
Video: Allomyces Zoospores

59. © 2014 Pearson Education, Inc.
Figure 26.14
100 nm
Zone of arbuscule-
containing cells

60. © 2014 Pearson Education, Inc.
Figure 26.14a
100 nm
Zone of arbuscule-
containing cells

61. © 2014 Pearson Education, Inc.
Figure 26.14b

62. © 2014 Pearson Education, Inc.
 Molecular evidence suggests that genes required
for the establishment of mycorrhizal symbiosis were
present in the common ancestor to land plants

63. © 2014 Pearson Education, Inc.
Diversification of Fungi
 Molecular analyses have helped clarify evolutionary
relationships among fungal groups, although areas
of uncertainty remain
 There are about 100,000 known species of fungi, but
there are estimated to be as many as 1.5 million
species

64. © 2014 Pearson Education, Inc.
Figure 26.15
2.5 µm
Chytrids (1,000 species)
Zygomycetes (1,000 species)
Glomeromycetes (160 species)
Ascomycetes (65,000 species)
Basidiomycetes (30,000 species)
25 µm
Hyphae

65. © 2014 Pearson Education, Inc.
 Chytrids (1,000 species) are found in freshwater
and terrestrial habitats
 Chytrids have flagellated spores and are thought to
have diverged early in fungal evolution

66. © 2014 Pearson Education, Inc.
Figure 26.15a
Chytrids (1,000 species)
25 µm
Hyphae

67. © 2014 Pearson Education, Inc.
 Zygomycetes (1,000 species) include fast-growing
molds, parasites, and commensal symbionts

68. © 2014 Pearson Education, Inc.
Figure 26.15b
Zygomycetes (1,000 species)

69. © 2014 Pearson Education, Inc.
 Glomeromycetes (160 species) form arbuscular
mycorrhizae with plant roots
 About 80% of plant species have mutualistic
relationships with glomeromycetes

70. © 2014 Pearson Education, Inc.
Figure 26.15c
2.5 µm
Glomeromycetes (160 species)

71. © 2014 Pearson Education, Inc.
 Ascomycetes (65,000 species) live in marine,
freshwater, and terrestrial habitats
 Ascomycetes produce fruiting bodies called
ascocarps

72. © 2014 Pearson Education, Inc.
Figure 26.15d
Ascomycetes (65,000 species)

73. © 2014 Pearson Education, Inc.
 Basidiomycetes (30,000 species) are important
decomposers and ectomycorrhizal fungi
 The fruiting bodies of basidiomycetes are commonly
called mushrooms

74. © 2014 Pearson Education, Inc.
Figure 26.15e
Basidiomycetes (30,000 species)

75. © 2014 Pearson Education, Inc.
Concept 26.3: Early land plants radiated into a
diverse set of lineages
 Ancestral species gave rise to a vast diversity of
modern plants

76. © 2014 Pearson Education, Inc.
Figure 26.16
Origin of land plants
Origin of vascular plants
Origin of extant seed
plants
ANCESTRAL
GREEN
ALGA
Millions of years ago (mya)
500
Angiosperms
450 400 350 300 50 0
3
2
1
Gymnosperms
Mosses
Hornworts
Lycophytes (club
mosses, spike
mosses, quillworts)
Monilophytes (ferns,
horsetails, whisk ferns)
Liverworts
Landplants
Vascularplants
Seedplants
Seedless
vascular
plants
Nonvascular
plants
(bryophytes)

77. © 2014 Pearson Education, Inc.
Figure 26.16a
Origin of land plants
Origin of vascular plants
Origin of extant seed
plants
ANCESTRAL
GREEN
ALGA
Millions of years ago (mya)
500
Angiosperms
450 400 350 300 50 0
3
2
1
Gymnosperms
Mosses
Hornworts
Lycophytes
Monilophytes
Liverworts

78. © 2014 Pearson Education, Inc.
Figure 26.16b
Angiosperms
Gymnosperms
Mosses
Hornworts
Lycophytes (club
mosses, spike
mosses, quillworts)
Monilophytes (ferns,
horsetails, whisk ferns)
Liverworts
Landplants
Vascularplants
Seedplants
Seedless
vascular
plants
Nonvascular
plants
(bryophytes)

79. © 2014 Pearson Education, Inc.
 Land plants can be informally grouped based on the
presence or absence of vascular tissue
 Most plants have vascular tissue for the transport of
water and nutrients; these constitute the vascular
plants
 Nonvascular plants are commonly called
bryophytes

80. © 2014 Pearson Education, Inc.
Bryophytes: A Collection of Early Diverging Plant
Lineages
 Bryophytes are represented today by three clades
of small herbaceous (nonwoody) plants
 Liverworts
 Mosses
 Hornworts
 These three clades are thought to be the earliest
lineages diverged from the common ancestor of
land plants

81. © 2014 Pearson Education, Inc.
Figure 26.UN03
Angiosperms
Gymnosperms
Seedless vascular plants
Nonvascular plants (bryophytes)

82. © 2014 Pearson Education, Inc.
Figure 26.17
Sporophyte
Sporophyte
(a sturdy
plant that
takes months
to grow)
Gametophyte
Gametophyte
Capsule
Seta
(b) Polytrichum commune, a moss
(c) Anthoceros sp., a hornwort
(a) Plagiochila deltoidea, a
liverwort

83. © 2014 Pearson Education, Inc.
Figure 26.17a
(a) Plagiochila deltoidea, a
liverwort

84. © 2014 Pearson Education, Inc.
Figure 26.17b
Sporophyte
(a sturdy
plant that
takes months
to grow)
Gametophyte
Capsule
Seta
(b) Polytrichum commune, a moss

85. © 2014 Pearson Education, Inc.
Figure 26.17c
Sporophyte
Gametophyte
(c) Anthoceros sp., a hornwort

86. © 2014 Pearson Education, Inc.
 Bryophytes are anchored to the substrate by
rhizoids
 The flagellated sperm produced by bryophytes must
swim through a film of water to reach and fertilize the
egg
 In bryophytes, the gametophytes are larger and
longer-living than sporophytes
 The height of gametophytes is constrained by lack of
vascular tissues

87. © 2014 Pearson Education, Inc.
Seedless Vascular Plants: The First Plants to
Grow Tall
 Bryophytes were the prevalent vegetation during
the first 100 million years of plant evolution
 The earliest vascular plants date to 425–420 million
years ago
 Vascular tissue allowed these plants to grow tall
 Early vascular plants lacked seeds

88. © 2014 Pearson Education, Inc.
 Seedless vascular plants can be divided into
clades
– Lycophytes (club mosses and their relatives)
– Monilophytes (ferns and their relatives)
Video: Plant time Lapse

89. © 2014 Pearson Education, Inc.
Figure 26.UN04
Angiosperms
Gymnosperms
Seedless vascular plants
Nonvascular plants (bryophytes)

90. © 2014 Pearson Education, Inc.
Figure 26.18
(a) Diphasiastrum tristachyum, a
lycophyte
Strobili
(conelike
structures
in which
spores are
produced)
(b) Athyrium filix-femina, a
monilophyte
2.5 cm 2.5 cm

91. © 2014 Pearson Education, Inc.
Figure 26.18a
(a) Diphasiastrum tristachyum, a
lycophyte
Strobili
(conelike
structures
in which
spores are
produced)
2.5 cm

92. © 2014 Pearson Education, Inc.
Figure 26.18b
(b) Athyrium filix-femina, a
monilophyte
2.5 cm

93. © 2014 Pearson Education, Inc.
Life Cycles with Dominant Sporophytes
 In contrast with bryophytes, sporophytes of seedless
vascular plants are the larger generation, as in
familiar ferns
 The gametophytes are tiny plants that grow on or
below the soil surface
 Flagellated sperm must swim through a film of water
to reach eggs
Animation: Pine Life Cycle

94. © 2014 Pearson Education, Inc.
Figure 26.19
Sporophyte
Gametophyte
Example
PLANT GROUP
Mosses and other
nonvascular plants
Ferns and other
seedless
vascular plants
Reduced, independent
(photosynthetic and
free-living)
Reduced (usually microscopic), dependent on
surrounding sporophyte tissue for nutrition
Seed plants (gymnosperms and angiosperms)
Dominant
Dominant Dominant
Reduced, dependent
on gametophyte for
nutrition
Gametophyte
(n)
Gametophyte
(n)
Sporophyte
(2n)
Sporophyte
(2n)
Sporophyte (2n) Sporophyte (2n)
Gymnosperm Angiosperm
Microscopic female
gametophytes (n) inside
ovulate cone Microscopic female
gametophytes
(n) inside these parts
of flowers
Microscopic
male
gametophytes
(n) inside
these parts
of flowersMicroscopic
male
gametophytes (n)
inside pollen
cone

95. © 2014 Pearson Education, Inc.
Figure 26.19a
Sporophyte
Gametophyte
Example
Mosses and other
nonvascular plants
Dominant
Reduced, dependent on
gametophyte for nutrition
Gametophyte
(n)
Sporophyte
(2n)

96. © 2014 Pearson Education, Inc.
Figure 26.19b
Sporophyte
Gametophyte
Example
Ferns and other seedless
vascular plants
Reduced, independent
(photosynthetic and free-living)
Dominant
Gametophyte (n)
Sporophyte
(2n)

97. © 2014 Pearson Education, Inc.
Figure 26.19c
Sporophyte
Gametophyte
Example
Reduced (usually microscopic), dependent on
surrounding sporophyte tissue for nutrition
Seed plants (gymnosperms and angiosperms)
Dominant
Sporophyte (2n)
Gymnosperm
Microscopic female
gametophytes (n)
inside ovulate
cone
Microscopic male
gametophytes (n)
inside pollen cone

98. © 2014 Pearson Education, Inc.
Figure 26.19d
Sporophyte
Gametophyte
Example
Reduced (usually microscopic), dependent on
surrounding sporophyte tissue for nutrition
Seed plants (gymnosperms and angiosperms)
Dominant
Sporophyte (2n)
Angiosperm
Microscopic female gametophytes
(n) inside these parts
of flowers
Microscopic male
gametophytes (n)
inside these
parts of flowers

99. © 2014 Pearson Education, Inc.
Transport in Xylem and Phloem
 Vascular plants have two types of vascular tissue:
xylem and phloem
 Xylem conducts most of the water and minerals and
includes tube-shaped cells called tracheids
 Water-conducting cells are strengthened by lignin
and provide structural support
 Phloem consists of cells arranged in tubes that
distribute sugars, amino acids, and other organic
products

100. © 2014 Pearson Education, Inc.
 Vascular tissue allowed for increased height, which
provided an evolutionary advantage
 Tall plants were better competitors for sunlight and
could disperse spores much farther than short plants

101. © 2014 Pearson Education, Inc.
Evolution of Roots and Leaves
 Roots are organs that anchor vascular plants
 They enable vascular plants to absorb water and
nutrients from the soil

102. © 2014 Pearson Education, Inc.
 Leaves are organs that increase the surface area of
vascular plants, thereby capturing more solar energy
that is used for photosynthesis
 Leaves are categorized by two types
 Microphylls, small leaves with a single vein
 Megaphylls, larger, more productive leaves with a
highly branched vascular system

103. © 2014 Pearson Education, Inc.
 Seedless vascular plants were abundant in the
Carboniferous period (359–299 million years ago)
 Early seed plants rose to prominence at the end of
the Carboniferous period

104. © 2014 Pearson Education, Inc.
Concept 26.4: Seeds and pollen grains are key
adaptations for life on land
 Seed plants originated about 360 million years ago
 An adaptation called the seed allowed them to
expand into diverse terrestrial habitats
 A seed consists of an embryo and its food supply,
surrounded by a protective coat
 Mature seeds are dispersed by wind or other means

105. © 2014 Pearson Education, Inc.
 Extant seed plants are divided into two clades
 Gymnosperms have “naked” seeds that are not
enclosed in chambers
 Angiosperms have seeds that develop inside
chambers called ovaries

106. © 2014 Pearson Education, Inc.
Figure 26.UN05
Angiosperms
Gymnosperms
Seedless vascular plants
Nonvascular plants (bryophytes)

107. © 2014 Pearson Education, Inc.
Terrestrial Adaptations in Seed Plants
 In addition to seeds, the following are common to all
seed plants:
 Reduced gametophytes
 Ovules
 Pollen

108. © 2014 Pearson Education, Inc.
Reduced Gametophytes
 The gametophytes of seed plants are microscopic
 Gametophytes develop within the walls of spores
that are retained within tissues of the parent
sporophyte
 The parent sporophyte protects and provides
nutrients to the developing gametophyte

109. © 2014 Pearson Education, Inc.
Ovules and Pollen
 An ovule consists of an egg-producing female
gametophyte surrounded by a protective layer of
sporophyte tissue called the integument
 Female gametophytes develop from large
megaspores

110. © 2014 Pearson Education, Inc.
Figure 26.20-1
Immature
ovulate cone
Megaspore (n)
Integument (2n)
Spore wall
Megasporangium
(2n)
Pollen
grain (n)Micropyle
(a) Unfertilized ovule

111. © 2014 Pearson Education, Inc.
Figure 26.20-2
Pollen tube
Female
gametophyte (n)
Egg nucleus
(n)
Discharged
sperm nucleus
(n)
Male
gametophyte
Immature
ovulate cone
Megaspore (n)
Integument (2n)
Spore wall
Megasporangium
(2n)
Pollen
grain (n)Micropyle
(a) Unfertilized ovule (b) Fertilized ovule

112. © 2014 Pearson Education, Inc.
Figure 26.20-3
Pollen tube
Female
gametophyte (n)
Seed coat
Spore
wall
Food
supply
(n)
Embryo (2n)
Egg nucleus
(n)
Discharged
sperm nucleus
(n)
Male
gametophyte
Immature
ovulate cone
Megaspore (n)
Integument (2n)
Spore wall
Megasporangium
(2n)
Pollen
grain (n)Micropyle
(a) Unfertilized ovule (b) Fertilized ovule (c) Gymnosperm seed

113. © 2014 Pearson Education, Inc.
 Male gametophytes develop from small microspores
 Microspores develop into pollen grains, which
consist of a male gametophyte enclosed within the
protective pollen wall
 Pollination is the transfer of pollen to the part of a
seed plant containing the ovules
 Pollen eliminates the need for a film of water and can
be dispersed great distances by air or animals

114. © 2014 Pearson Education, Inc.
The Evolutionary Advantage of Seeds
 A seed develops from the whole ovule
 A seed is a sporophyte embryo, along with its food
supply, packaged in a protective coat

115. © 2014 Pearson Education, Inc.
 Seeds provide some evolutionary advantages over
spores
 They may remain dormant from days to years, until
conditions are favorable for germination
 Seeds have a supply of stored food

116. © 2014 Pearson Education, Inc.
Early Seed Plants and the Rise of Gymnosperms
 Fossil evidence reveals that by the late Devonian
period, some plants had begun to acquire features
found in seed plants but did not bear seeds
 Gymnosperms appeared in the fossil record about
305 million years ago
 Gymnosperms largely replaced nonvascular plants
as the climate became drier toward the end of the
Carboniferous period

117. © 2014 Pearson Education, Inc.
 Gymnosperms were better suited than nonvascular
plants to drier conditions due to adaptations
including
 Seeds and pollen
 Thick cuticles
 Leaves with small surface area

118. © 2014 Pearson Education, Inc.
 Gymnosperms are an important part of Earth’s flora
 For example, vast regions in northern latitudes are
covered by forests of cone-bearing gymnosperms
called conifers
Video: Flower Time Lapse

119. © 2014 Pearson Education, Inc.
Figure 26.21
(b) Douglas fir (Pseudotsuga
menziesii)
(a) Sago palm (Cycas revoluta)
(c) Creeping juniper (Juniperus
horizontalis)

120. © 2014 Pearson Education, Inc.
Figure 26.21a
(a) Sago palm (Cycas revoluta)

121. © 2014 Pearson Education, Inc.
Figure 26.21b
(b) Douglas fir (Pseudotsuga menziesii)

122. © 2014 Pearson Education, Inc.
Figure 26.21c
(c) Creeping juniper (Juniperus horizontalis)

123. © 2014 Pearson Education, Inc.
The Origin and Diversification of Angiosperms
 Angiosperms are seed plants with reproductive
structures called flowers and fruits
 They are the most widespread and diverse of all
plants

124. © 2014 Pearson Education, Inc.
Flowers and Fruits
 The flower is an angiosperm structure specialized
for sexual reproduction
 Many species are pollinated by insects or animals,
while some species are wind-pollinated

125. © 2014 Pearson Education, Inc.
 A flower is a specialized shoot with up to four types
of modified leaves called floral organs
 Sepals, which enclose the flower
 Petals, which are brightly colored and attract
pollinators
 Stamens, which produce pollen
 Carpels, which produce ovules

126. © 2014 Pearson Education, Inc.
Figure 26.22
Sepal
Ovule
Petal
Style
Ovary
Stigma
Carpel
Stamen
Filament
Anther

127. © 2014 Pearson Education, Inc.
 A stamen consists of a stalk called a filament, with a
sac called an anther where the pollen is produced
 A carpel consists of an ovary at the base and a style
leading up to a stigma, where pollen is received
 The ovary contains one or more ovules

128. © 2014 Pearson Education, Inc.
 Seeds develop from ovules after fertilization
 The ovary wall thickens and matures to form a fruit
 Fruits protect seeds and aid in their dispersal

129. © 2014 Pearson Education, Inc.
 Various fruit adaptations help disperse seeds by
wind, water, or animals
 Fruits can function as
 Parachutes or propellers for wind dispersal
 Burrs that cling to animal fur or human clothing
 Food that is carried in the digestive system of animals
with seeds passing unharmed when the animal
defecates

130. © 2014 Pearson Education, Inc.
Angiosperm Evolution
 Darwin called the origin of angiosperms an
“abominable mystery”
 Fossil evidence and phylogenetic analysis have led
to progress in solving the mystery, but we still do not
fully understand the evolution of angiosperms

131. © 2014 Pearson Education, Inc.
 Fossil evidence: Angiosperms originated at least
140 million years ago and dominated the landscape
by the end of the Cretaceous period, 65 million
years ago
 Chinese fossils of 125-million-year-old angiosperms
help us to infer traits of the angiosperm common
ancestor
 Archaefructus sinensis, for example, was
herbaceous and may have been aquatic

132. © 2014 Pearson Education, Inc.
Figure 26.23
Carpel
Stamen
(a) Archaefructus sinensis, a
125-million-year-old fossil
(b) Artist’s reconstruction of
Archaefructus sinensis
5 cm

133. © 2014 Pearson Education, Inc.
Figure 26.23a
(a) Archaefructus sinensis, a
125-million-year-old fossil
5 cm

134. © 2014 Pearson Education, Inc.
 Angiosperm phylogeny: The ancestors of
angiosperms and gymnosperms diverged about
305 million years ago
 Angiosperms may be closely related to Bennettitales,
extinct seed plants with flowerlike structures

135. © 2014 Pearson Education, Inc.
Figure 26.24
Microsporangia
(contain
microspores)
Ovules

136. © 2014 Pearson Education, Inc.
 Amborella and water lilies are likely descended from
two of the most ancient angiosperm lineages

137. © 2014 Pearson Education, Inc.
Figure 26.25
Most recent common ancestor
of all living angiosperms
Magnoliids Monocots
Eudicots
Star anise
Water liliesAmborella
Amborella
Star anise
and relatives
Water lilies
Magnoliids
Monocots
Eudicots
Millions of years ago
150 125 100 25 0

138. © 2014 Pearson Education, Inc.
Figure 26.25a
Most recent common ancestor
of all living angiosperms
Amborella
Star anise
and relatives
Water lilies
Magnoliids
Monocots
Eudicots
Millions of years ago
150 125 100 25 0

139. © 2014 Pearson Education, Inc.
Figure 26.25b
Amborella Star aniseWater lilies
Magnoliids Monocots
Eudicots

140. © 2014 Pearson Education, Inc.
 Amborella includes only one known species, a
small shrub called Amborella trichopoda

141. © 2014 Pearson Education, Inc.
Figure 26.25ba
Amborella

142. © 2014 Pearson Education, Inc.
 Water lilies are found in aquatic habitats throughout
the world

143. © 2014 Pearson Education, Inc.
Figure 26.25bb
Water lilies

144. © 2014 Pearson Education, Inc.
 Star anise naturally occur in southeast Asia and the
southeastern United States
 Extant species are likely descended from ancestral
populations that were separated by continental drift

145. © 2014 Pearson Education, Inc.
Figure 26.25bc
Star anise

146. © 2014 Pearson Education, Inc.
 Magnoliids include magnolias, laurels, avocado,
cinnamon, and black pepper plants

147. © 2014 Pearson Education, Inc.
Figure 26.25bd
Magnoliids

148. © 2014 Pearson Education, Inc.
 Monocots account for more than one-quarter of
angiosperm species

149. © 2014 Pearson Education, Inc.
Figure 26.25be
Monocots

150. © 2014 Pearson Education, Inc.
 Eudicots account for more than two-thirds of
angiosperm species

151. © 2014 Pearson Education, Inc.
Figure 26.25bf
Eudicots

152. © 2014 Pearson Education, Inc.
Concept 26.5: Land plants and fungi
fundamentally changed chemical cycling and
biotic interactions
 The colonization of land by plants and fungi altered
the physical environment and the organisms that
live there

153. © 2014 Pearson Education, Inc.
Physical Environment and Chemical Cycling
 A lichen is a symbiotic association between a
photosynthetic microorganism and a fungus
 Lichens are important pioneers on new rock and soil
surfaces
 They break down the surface, affecting the formation
of soil and making it possible for plants to grow
 Lichens may have helped the colonization of land by
plants

154. © 2014 Pearson Education, Inc.
Figure 26.26
A foliose (leaflike) lichen
Crustose
(encrusting) lichens
(b) Anatomy of a lichen involving an ascomycete fungus
and an alga
(a) Two common lichen growth forms
Fungal hyphae
Algal cell
50µm

155. © 2014 Pearson Education, Inc.
Figure 26.26a
A foliose (leaflike) lichen
Crustose
(encrusting) lichens
(a) Two common lichen growth forms

156. © 2014 Pearson Education, Inc.
Figure 26.26aa
Crustose (encrusting) lichens

157. © 2014 Pearson Education, Inc.
Figure 26.26ab
A foliose (leaflike) lichen

158. © 2014 Pearson Education, Inc.
Figure 26.26b
(b) Anatomy of a lichen involving an ascomycete fungus
and an alga
Fungal hyphae
Algal cell
50µm

159. © 2014 Pearson Education, Inc.
Figure 26.26ba
Fungal hyphae
Algal cell
50µm

160. © 2014 Pearson Education, Inc.
 Plants affect the formation of soil
 Roots hold the soil in place
 Leaf litter and other decaying plant parts add
nutrients to the soil
 Plants have also altered Earth’s atmosphere by
releasing oxygen to the air through photosynthesis

161. © 2014 Pearson Education, Inc.
 Plants and fungi affect the cycling of chemicals in
ecosystems
 Plants absorb nutrients, which are passed on to the
animals that eat them
 Decomposers, including fungi and bacteria, break
down dead organisms and return nutrients to the
physical environment

162. © 2014 Pearson Education, Inc.
 Plants play an important role in carbon recycling
 Photosynthesis removes CO2 from the atmosphere
 Increased growth and accelerated photosynthesis
resulted from the formation of vascular tissue and
may have contributed to global cooling at the end of
the Carboniferous period

163. © 2014 Pearson Education, Inc.
Figure 26.27
Lycophyte trees HorsetailFern
Lycophyte tree
reproductive
structures
Tree trunk covered
with small leaves

164. © 2014 Pearson Education, Inc.
Biotic Interactions
 Biotic interactions can benefit both species involved
(mutualisms) or be beneficial to one species while
harming the other (as when a parasite feeds on its
host)
 Plants and fungi had large effects on biotic
interactions because they increased the available
energy and nutrients on land

165. © 2014 Pearson Education, Inc.
Fungi as Mutualists and Pathogens
 Mutualistic fungi absorb nutrients from a host
organism and reciprocate with actions that benefit
the host
 Plants harbor harmless symbiotic endophytes, fungi
that live inside leaves or other plant parts
 Endophytes make toxins that deter herbivores and
defend against pathogens

166. © 2014 Pearson Education, Inc.
Figure 26.28
Endophyte not present; pathogen present (E−P+)
Both endophyte and pathogen present (E+P+)
E−P+E−P+ E+P+ E+P+
15
10
5
0
Leafmortality(%)
Leafareadamaged(%)
30
20
10
0
Results

167. © 2014 Pearson Education, Inc.
 Parasitic fungi absorb nutrients from host cells, but
provide no benefits in return
 About 30% of known fungal species are parasites or
pathogens, mostly on or in plants
 For example, Cryphonectria parasitica causes
chestnut blight

168. © 2014 Pearson Education, Inc.
Figure 26.29
(a) Corn smut on corn
(c) Ergots on rye
(b) Tar spot
fungus
on maple
leaves

169. © 2014 Pearson Education, Inc.
Figure 26.29a
(a) Corn smut on corn

170. © 2014 Pearson Education, Inc.
Figure 26.29b
(b) Tar spot fungus on maple
leaves

171. © 2014 Pearson Education, Inc.
Figure 26.29c
(c) Ergots on rye

172. © 2014 Pearson Education, Inc.
Plant-Animal Interactions
 Animals influence the evolution of plants, and vice
versa
 For example, animal herbivory selects for plant
defenses
 For example, interactions between pollinators and
flowering plants select for mutually beneficial
adaptations

173. © 2014 Pearson Education, Inc.
 Clades with bilaterally symmetrical flowers have
more species than those with radially symmetrical
flowers
 This is likely because bilateral symmetry affects the
movement of pollinators and reduces gene flow in
diverging populations

174. © 2014 Pearson Education, Inc.
Figure 26.UN06
Bilateral symmetry
Time since divergence
from common ancestor
Radial symmetry
Common
ancestor “Bilateral” clade
“Radial” clade
Compare
numbers
of species

175. © 2014 Pearson Education, Inc.
 Angiosperms and other plant groups are being
threatened by the exploding human population and
its demand for space and resources
 About 55,000 km2
of tropical rain forest are cleared
each year
 Deforestation leads to the extinction of plant, insect
and other animal species
 If current extinction rates continue, more than 50%
of Earth’s species will be lost within the next few
centuries

176. © 2014 Pearson Education, Inc.
Figure 26.30
(b) By 2009, much more
of this same tropical
forest had been cut
down.
(a) A satellite image from
2000 shows clear-cut
areas in Brazil (brown)
surrounded by dense
tropical forest (green).
4km

177. © 2014 Pearson Education, Inc.
Figure 26.30a
(a) A satellite image from
2000 shows clear-cut
areas in Brazil (brown)
surrounded by dense
tropical forest (green).
4km

178. © 2014 Pearson Education, Inc.
Figure 26.30b
(b) By 2009, much more
of this same tropical
forest had been cut
down.
4km

179. © 2014 Pearson Education, Inc.
Figure 26.UN02a
No AM fungi
Thermal AM fungi
Nonthermal AM fungi
Soil treatment
Shootdryweight(g)
0.4
0.3
0.2
0.1
0.0

180. © 2014 Pearson Education, Inc.
Figure 26.UN02b

181. © 2014 Pearson Education, Inc.
Figure 26.UN02c
Root length
Soil temperature (°C)
Rootlength(cm/g)
50
40
30
20
10
Hyphal length
0
5
4
3
2
1
0
Hyphallength(m/g)
35 403020 250 45

182. © 2014 Pearson Education, Inc.
Figure 26.UN07
FERTILIZATIONMEIOSIS
Alternation of generations
Mitosis
Gametophyte
Mitosis
Spore
Gamete
Zygote
Mitosis
Sporophyte
Haploid
Diploid
2n
n
n
n
n
SporesSporangium
Walled spores
in sporangia
21

183. © 2014 Pearson Education, Inc.
Figure 26.UN08
Sepal
Ovule
Petal
Style
Ovary
Stigma
Carpel (produces ovules)
Stamen
(produces pollen)
Filament
Anther
Flower anatomy

184. © 2014 Pearson Education, Inc.
Figure 26.UN09
Angiosperms
Gymnosperms
Mosses
Charophyte green algae
Ferns

185. © 2014 Pearson Education, Inc.
Figure 26.UN10