2. Land plants evolved from green algae
Green algae called charophyceans are the closest relatives of land plants
Comparisons of both nuclear and chloroplast genes point to charophyceans as the closest living relatives of land plants

3. Morphological and Biochemical Evidence
Many characteristics of land plants also appear in a variety of algal clades, mainly algae
However, land plants share four key traits only with charophyceans:
Rose-shaped complexes for cellulose synthesis
Peroxisome enzymes
Structure of flagellated sperm
Formation of a phragmoplast

4. Chara,
a pond
organism
(LM).
10 mm
40 µm
Coleochaete orbicularis, a disk-shaped
charophycean (LM).

5. Adaptations Enabling the Move to Land
In charophyceans a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out
The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants
Many adaptations emerged after land plants diverged from their charophycean relatives

6. Defining the Plant Kingdom
Systematists are currently debating the boundaries of the plant kingdom
Some biologists think the plant kingdom should be expanded to include some or all green algae
Until this debate is resolved, we will retain the embryophyte definition of kingdom Plantae

7. Viridiplantae
Streptophyta
Plantae
Red algae
Chlorophytes
Charophyceans
Embryophytes
Ancestral alga

8. Derived Traits of Plants
Five key traits appear in nearly all land plants but are absent in the charophyceans:
Apical meristems
Alternation of generations
Walled spores produced in sporangia
Multicellular gametangia
Multicellular dependent embryos

9. Apical Meristems Apical Meristem of shoot Developing leaves
Root
100 µm
100 µm

10. Alternation of Generations
Haploid multicellular
organism (gametophyte)
Mitosis
Mitosis
Spores
Gametes
MEIOSIS
FERTILIZATION
Zygote
Mitosis
Diploid multicellular
organism (sporophyte)

11. Walled Spores Produced in Sporangia Multicellular Gametangia
Dependent Embryos
Longitudinal section of
Sphagnum sporangium (LM)
Archegonium
with egg
Female gametophyte
Spores
Embryo
Maternal
tissue
Sporangium
2 µm
10 µm
Sporophyte
Male gametophyte
Antheridium
with sperm
Gametophyte
Wall
ingrowths
Placental
transfer
cell
Sporophyte and sporangium
of Sphagnum (a moss)
Archegonia and antheridia
of Marchantia (a liverwort)

12. Additional derived traits such as a cuticle and secondary compounds evolved in many plant species

13. The Origin and Diversification of Plants
Fossil evidence indicates that plants were on land at least 475 million years ago
Fossilized spores and tissues have been extracted from 475-million-year-old rocks
Those ancestral species gave rise to a vast diversity of modern plants
Land plants can be informally grouped based on the presence or absence of vascular tissue

14. Fossilized spores. Unlike the spores of most living plants, which are single grains, these spores found in Oman are in groups of four (left; one hidden) and two (right).
Fossilized sporophyte tissue. The spores were embedded in tissue that appears to be from plants.

16. Seedless vascular plants Origin of vascular plants
Land plants
Vascular plants
Bryophytes
Seedless vascular plants
Seed plants
Gymno-
sperms
Angio-
sperms
Liverworts
Hornworts
Mosses
Lycophytes
Pterophytes
Charophyceans
Origin of seed plants
(about 360 mya)
Origin of vascular plants
(about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga

17. The life cycles of mosses and other bryophytes are dominated by the gametophyte stage
Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants:
Liverworts, phylum Hepatophyta
Hornworts, phylum Anthocerophyta
Mosses, phylum Bryophyta
Mosses are most closely related to vascular plants

18. Bryophyte Gametophytes
In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes
Bryophyte gametophytes
Produce flagellated sperm in antheridia
Produce ova in archegonia
Generally form ground-hugging carpets and are at most only a few cells thick
Some mosses have conducting tissues in the center of their “stems” and may grow vertically

19. Raindrop
Key
Male
gametophyte
Haploid (n)
Sperm
Diploid (2n)
Spores develop into
threadlike protonemata.
“Bud”
A sperm swims through a film of moisture to an archegonium and fertilizes the egg.
Antheridia
The haploid protonemata produce “buds” that grow into gametophytes.
Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively.
Protonemata
“Bud”
Egg
Spores
Gametophore
Female
gametophyte
Archegonia
Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores.
Rhizoid
Peristome
Sporangium
The sporophyte grows a long stalk, or seta, that emerges from the archegonium.
FERTILIZATION
MEIOSIS
(within archegonium)
Seta
Calyptra
Capsule
(sporangium)
Zygote
Mature
sporophytes
Foot
Embryo
Archegonium
The diploid zygote develops into a sporophyte embryo within the archegonium.
Young
sporophyte
Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte.
Capsule with
peristome (SEM)
Female
gametophytes

20. Bryophyte Sporophytes
Grow out of archegonia
Are the smallest and simplest of all extant plant groups
Consist of a foot, a seta, and a sporangium
Hornwort and moss sporophytes have stomata

21. Gametophore of
female gametophyte
500 µm
Foot
Seta
Sporangium
Marchantia polymorpha,
a “thalloid” liverwort
Marchantia sporophyte (LM)

22. Plagiochila
deltoidea,
a “leafy”
liverwort

23. An Anthroceros
hornwort species
Sporophyte
Gametophyte

24. Polytrichum
commune,
hairy cap
moss
Sporophyte
Gametophyte

25. Ecological and Economic Importance of Mosses
Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat
Sphagnum plays an important role in the Earth’s carbon cycle

26. A peat bog.
Gametophyte
Sporangium at
tip of sporophyte
Living
photo-
synthetic
cells
Dead water-
storing cells
100 µm
Closeup of Sphagnum.
Note the “leafy”
Gametophytes and their offspring, the sporophytes.
Sphagnum “leaf” (LM). The combination of living photosynthetic cells and dead water-storing cells gives the moss its spongy quality.
“Tolland Man,” a bog mummy dating from 405–100 B.C. The acidic, oxygen-poor conditions produced by Sphagnum can preserve human or animal bodies for thousands of years.

27. Ferns and other seedless vascular plants formed the first forests
Bryophytes and bryophyte-like plants were the prevalent vegetation during the first 100 million years of plant evolution
Vascular plants began to diversify during the Carboniferous period
Vascular plants dominate most landscapes today

28. Origins and Traits of Vascular Plants
Fossils of the forerunners of vascular plants date back about 420 million years
These early tiny plants had independent, branching sporophytes
They lacked other derived traits of vascular plants

30. Life Cycles with Dominant Sporophytes
In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern
The gametophytes are tiny plants that grow on or below the soil surface

31. Key
Haploid (n)
Diploid (2n)
Spore
Young
gametophyte
Antheridium
MEIOSIS
Sporangium
Sperm
Archegonium
Egg
New
sporophyte
Sporangium
Mature
sporophyte
Zygote
FERTILIZATION
Sorus
Gametophyte
Fiddlehead

32. 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 dead cells called tracheids
Phloem consists of living cells and distributes sugars, amino acids, and other organic products

33. Evolution of Roots Roots are organs that anchor vascular plants
They enable vascular plants to absorb water and nutrients from the soil
Roots may have evolved from subterranean stems

34. Evolution of Leaves
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, leaves with a single vein
Megaphylls, leaves with a highly branched vascular system
According to one model of evolution, microphylls evolved first, as outgrowths of stems

35. Vascular tissue
Microphylls
Megaphylls

36. Sporophylls and Spore Variations
Sporophylls are modified leaves with sporangia
Most seedless vascular plants are homosporous, producing one type of spore that develops into a bisexual gametophyte
All seed plants and some seedless vascular plants are heterosporous, having two types of spores that give rise to male and female gametophytes

38. Classification of Seedless Vascular Plants
There are two phyla of seedless vascular plants:
Lycophyta includes club mosses, spike mosses, and quillworts
Pterophyta includes ferns, horsetails, and whisk ferns and their relatives

39. Selaginella apoda,
a spike moss

40. Isoetes
gunnii,
a quillwort

41. Strobili
(clusters of
sporophyllis)
Diphasiastrum tristachyum, a club moss

42. Psilotum
nudum,
a whisk
fern

43. Equisetum
arvense,
field
horsetail
Vegetative stem
Strobilus on
fertile stem

44. Athyrium filix-femina, lady fern

45. Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts
Giant lycophytes thrived for millions of years in moist swamps
Surviving species are small herbaceous plants

46. Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives
Ferns are the most diverse seedless vascular plants, with more than 12,000 species
They are most diverse in the tropics but also thrive in temperate forests
Some species are even adapted to arid climates

47. The Significance of Seedless Vascular Plants
The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Carboniferous, forming the first forests
These forests may have helped produce the global cooling at the end of the Carboniferous period
The decaying plants of these Carboniferous forests eventually became coal

48. Animations and Videos Life Cycle of a Moss – 1
Life Cycle of a Fern
Chapter Quiz Questions – 1
Chapter Quiz Questions - 2

49. Which of the following are the closest algal relatives of land plants?
psilophytes
charophytes
chrysophytes
bacillariophytes
rhodophytes
Answer: b

50. Which of the following are the closest algal relatives of land plants?
psilophytes
charophytes
chrysophytes
bacillariophytes
rhodophytes 50

51. The relationship between a gametophyte and a sporophyte in a liverwort is like the relationship between
a brother and a sister.
a grandparent and a grandchild.
an uncle and a nephew.
a parent and a child.
two cousins.
Answer: d 51

52. The relationship between a gametophyte and a sporophyte in a liverwort is like the relationship between
a brother and a sister.
a grandparent and a grandchild.
an uncle and a nephew.
a parent and a child.
two cousins. 52

53. Plants that evolved vascular tissue are more advanced than plants without vascular tissue. One of the consequences is that vascular tissue enabled plants to
reproduce via spores.
store water.
grow taller.
develop stomata.
support large gametophytes.
Answer: c 53

54. Plants that evolved vascular tissue are more advanced than plants without vascular tissue. One of the consequences is that vascular tissue enabled plants to
reproduce via spores.
store water.
grow taller.
develop stomata.
support large gametophytes. 54

55. One thing you should be able to conclude from this figure is that
gametophytes have fewer chromosomes than sporophytes do.
gametophytes evolved before sporophytes.
gametophytes grow from sporophytes.
gametophyte cells come about by mitosis; sporophyte cells come about by meiosis.
Answer: a
Gametophytes, being haploid, have half as many chromosomes as diploid sporophytes do. 55

56. One thing you should be able to conclude from this figure is that
gametophytes have fewer chromosomes than sporophytes do.
gametophytes evolved before sporophytes.
gametophytes grow from sporophytes.
gametophyte cells come about by mitosis; sporophyte cells come about by meiosis. 56

57. Stomata are found in every group of sporophyte plants except the liverworts. According to the hypothesis that stomata evolved only once among the bryophytes, this is evidence that
liverworts resemble the most primitive plants.
liverworts don’t need to exchange gases with the atmosphere.
liverworts have lost the ability to make stomata.
liverworts are able to fix nitrogen.
gametophytes are more important in liverworts.
Answer: a 57

58. Stomata are found in every group of sporophyte plants except the liverworts. According to the hypothesis that stomata evolved only once among the bryophytes, this is evidence that
liverworts resemble the most primitive plants.
liverworts don’t need to exchange gases with the atmosphere.
liverworts have lost the ability to make stomata.
liverworts are able to fix nitrogen.
gametophytes are more important in liverworts. 58

59. Which of the following plants have a sporophyte that is nutritionally dependent on the photosynthetic gametophyte?
ferns
mosses
whisk ferns
horsetails
Answer: b
The moss life cycle involves the growth of a brown, nutritionally dependent sporophyte out of the top of the photosynthetic gametophyte. 59

60. Which of the following plants have a sporophyte that is nutritionally dependent on the photosynthetic gametophyte?
ferns
mosses
whisk ferns
horsetails 60

61. Which of the following evolutionary innovation of seed plants enabled them to outcompete ferns and other seedless plants that dominated through the end of the Carboniferous period?
heterospory
reduced, dependent gametophytes
vascular systems
flowers
Answer: b 61

62. Which of the following evolutionary innovation of seed plants enabled them to outcompete ferns and other seedless plants that dominated through the end of the Carboniferous period?
heterospory
reduced, dependent gametophytes
vascular systems
flowers 62

63. Seedless vascular plants affected Earth and its other life in all of the following ways except
early forests contributed to a large drop in CO2 levels.
CO2 removed from the air was stored in marine rocks.
seedless vascular plants forming the first forests became coal.
plants reduce the rate at which chemicals such as calcium and magnesium are released from socks into soil.
Answer: d

64. Seedless vascular plants affected Earth and its other life in all of the following ways except
early forests contributed to a large drop in CO2 levels.
CO2 removed from the air was stored in marine rocks.
seedless vascular plants forming the first forests became coal.
plants reduce the rate at which chemicals such as calcium and magnesium are released from socks into soil.

65. Which of the following are not considered a nonvascular plant?
liverworts
mosses
hornworts
bryophytes
lycophytes
Answer: e

66. Which of the following are not considered a nonvascular plant?
liverworts
mosses
hornworts
bryophytes
lycophytes

67. Which term is correctly matched with its definition?
Sporophylls—modified leaves that bear sporangia
Strobili—cone-like structures formed from groups of sporophylls in lycophytes and gymnosperms
Sori—clusters of sporangia produced by fern sporophylls
Megaspores—develop into male gametophytes
Answer: d

68. Which term is correctly matched with its definition?
Sporophylls—modified leaves that bear sporangia
Strobili—cone-like structures formed from groups of sporophylls in lycophytes and gymnosperms
Sori—clusters of sporangia produced by fern sporophylls
Megaspores—develop into male gametophytes

69. Scientific Skills Exercises
Researchers set up experimental and control microcosms, or small artificial ecosystems, to measure the release of minerals from rocks. First, they placed rock fragments of volcanic origin, either granite or andesite, into small glass containers. Then they made a suspension of water and macerated (chopped and crushed) moss of the species Physcomitrella patens. They added this mixture of water and moss to the experimental microcosms. For the control microcosms, they filtered out the moss and just added the water.
After 130 days, they measured the amounts of various minerals found in the water in the control microcosms and in the water and moss in the experimental microcosms.

70. How did the setup of the control and experimental microcosms differ?
Control microcosms did not contain living moss, while experimental microcosms did contain living moss.
Control microcosms contained minerals in the water, while experimental microcosms did not contain minerals in the water.
Control microcosms did not contain rock of volcanic origin, while experimental microcosms did contain rock of volcanic origin.
Control microcosms contained water, while experimental microcosms did not contain water.
Answer: a

71. How did the setup of the control and experimental microcosms differ?
Control microcosms did not contain living moss, while experimental microcosms did contain living moss.
Control microcosms contained minerals in the water, while experimental microcosms did not contain minerals in the water.
Control microcosms did not contain rock of volcanic origin, while experimental microcosms did contain rock of volcanic origin.
Control microcosms contained water, while experimental microcosms did not contain water.

72. Why did the researchers add filtrate from which macerated moss had been removed to the control microcosms?
to control for the possibility that the filtrate contained material derived from moss
to control for the possibility that the filtrate included nutrients released from granite or andesite
to provide replication
to control for the possibility that the filtrate contained living moss cells
Answer: a

73. Why did the researchers add filtrate from which macerated moss had been removed to the control microcosms?
to control for the possibility that the filtrate contained material derived from moss
to control for the possibility that the filtrate included nutrients released from granite or andesite
to provide replication
to control for the possibility that the filtrate contained living moss cells
Answer: a

74. The bar graphs show the mean total amount of each element weathered from rocks in the control and experimental microcosms.
Answer: a

75. Overall, what is the effect of moss on the chemical weathering of rock?
Moss increases the chemical weathering of rock.
Moss does not increase the chemical weathering of rock.
It is not clear whether or not moss increases the chemical weathering of rock.
Answer: a

76. Overall, what is the effect of moss on the chemical weathering of rock?
Moss increases the chemical weathering of rock.
Moss does not increase the chemical weathering of rock.
It is not clear whether or not moss increases the chemical weathering of rock.

77. Why were mineral nutrients released in the control microcosms?
The release of mineral nutrients in the control microcosms indicates the extent of abiotic weathering of rock.
The release of mineral nutrients in the control microcosms indicates the extent of biotic weathering of rock.
The release of mineral nutrients in the control microcosms was due to organic acids released by mosses.
There was no release of mineral nutrients in the control microcosms.
Answer: a

78. Why were mineral nutrients released in the control microcosms?
The release of mineral nutrients in the control microcosms indicates the extent of abiotic weathering of rock.
The release of mineral nutrients in the control microcosms indicates the extent of biotic weathering of rock.
The release of mineral nutrients in the control microcosms was due to organic acids released by mosses.
There was no release of mineral nutrients in the control microcosms.

79. Review the earlier bar graph
Review the earlier bar graph. How does the moss’s chemical weathering effect on granite compare to the weathering effect on andesite?
Moss increased the release of all three elements (calcium, magnesium, and potassium) from both granite and andesite.
The results are not conclusive about the effect of moss on the chemical weathering of granite and andesite.
Moss did not alter the release of calcium, magnesium, and potassium from granite and andesite.
Moss decreased the release of all three elements (calcium, magnesium, and potassium) from both granite and andesite.
Answer: a

80. Review the earlier bar graph
Review the earlier bar graph. How does the moss’s chemical weathering effect on granite compare to the weathering effect on andesite?
Moss increased the release of all three elements (calcium, magnesium, and potassium) from both granite and andesite.
The results are not conclusive about the effect of moss on the chemical weathering of granite and andesite.
Moss did not alter the release of calcium, magnesium, and potassium from granite and andesite.
Moss decreased the release of all three elements (calcium, magnesium, and potassium) from both granite and andesite.

81. Based on their experimental results, the researchers added weathering of rock by nonvascular plants to simulation models of the Ordovician climate. The new models predicted decreased CO2 levels and global cooling sufficient to produce glaciations in the late Ordovician period. Which of the following assumptions did the researchers make in using results from their experiments in climate simulation models?
They assumed the modern moss P. patens increased the availability of mineral nutrients by breaking down granite and andesite.
They assumed that the effect of Ordovician mosses on the chemical weathering of rock was similar to the weathering caused by the modern moss P. patens.
They assumed that chemical weathering by mosses reduced atmospheric CO2 levels, producing dramatic climatic cooling in the late Ordovician period.
They assumed the modern moss P. patens increased the weathering of rock.
Answer: b

82. Based on their experimental results, the researchers added weathering of rock by nonvascular plants to simulation models of the Ordovician climate. The new models predicted decreased CO2 levels and global cooling sufficient to produce glaciations in the late Ordovician period. Which of the following assumptions did the researchers make in using results from their experiments in climate simulation models?
They assumed the modern moss P. patens increased the availability of mineral nutrients by breaking down granite and andesite.
They assumed that the effect of Ordovician mosses on the chemical weathering of rock was similar to the weathering caused by the modern moss P. patens.
They assumed that chemical weathering by mosses reduced atmospheric CO2 levels, producing dramatic climatic cooling in the late Ordovician period.
They assumed the modern moss P. patens increased the weathering of rock.
Answer: b

83. How do these experimental results and models demonstrate that life has profoundly changed Earth?
The results show that early nonvascular plants could have caused enough chemical weathering of rock to increase atmospheric CO2 levels.
The results show that nonvascular and vascular plants utilize rock-based minerals, including calcium, magnesium, and potassium.
The results show that mineral nutrients are released by the weathering of rock in the absence of living cells.
The results show that early nonvascular plants could have caused enough chemical weathering of rock to reduce atmospheric CO2 levels.
Answer: d

84. How do these experimental results and models demonstrate that life has profoundly changed Earth?
The results show that early nonvascular plants could have caused enough chemical weathering of rock to increase atmospheric CO2 levels.
The results show that nonvascular and vascular plants utilize rock-based minerals, including calcium, magnesium, and potassium.
The results show that mineral nutrients are released by the weathering of rock in the absence of living cells.
The results show that early nonvascular plants could have caused enough chemical weathering of rock to reduce atmospheric CO2 levels.