1. Plant Diversity I How Plants Colonized Land
Chapter 29
Plant Diversity I How Plants Colonized Land

2. Land Ho! The Greening of Earth
For the first 3 billion years of Earth’s history, the land was lifeless
Cyanobacteria existed on land about 1.2 billion years ago
~500 million years ago plants, fungi and animals joined them
DiversificationOver 290,00 species of plants inhabit Earth today

3. Plant Evolution Land plants evolved from green algae
Charophyceans (a type of green algae) are the closest relatives of land plants
Accumulation of adaptations to the terrestrial environment allowed the first land plants to live permanently above the waterline
Chara,
a pond
organism
(a)
10 mm
Coleochaete orbicularis
(b)
40 µm

4. Defining the Plant Kingdom
Systematists
Are currently debating the boundaries of the plant kingdom
Plantae
Streptophyta
Viridiplantae
Red algae
Chlorophytes
Charophyceans
Embryophytes
Ancestral alga

5. 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 (gametes produced here)
Multicellular dependent embryos

6. Apical meristems and alternation of generations
of shoot
Developing
leaves
100 µm
Apical meristem
of root
Root
Shoot .
APICAL MERISTEMS
Localized regions of cell division at tips of roots and shoots
Haploid multicellular
organism (gametophyte)
Mitosis
Gametes
Zygote
Diploid multicellular
organism (sporophyte)
Alternation of generations: a generalized scheme
MEIOSIS
FERTILIZATION 2n n
Spores
ALTERNATION OF GENERATIONS
Generations
Gametophyte (haploid)
Sporophyte (diploid)

7. Walled spores; multicellular gametangia; and multicellular, dependent embryos
WALLED SPORES PRODUCED IN SPORANGIA
Sporangium
Sporophyte and sporangium of Sphagnum (a moss)
Longitudinal section of
Sphagnum sporangium
Sporophyte
Gametophyte
MULTICELLULAR GAMETANGIA
(where gametes are produced)
Female gametophyte
Archegonium
with egg
Female gametangia (archegonia)
Male gametangia (antheridia)
Archegonia and antheridia of Marchantia (a liverwort)
Antheridium
with sperm
Male
gametophyte
MULTICELLULAR, DEPENDENT EMBRYOS
Embryo
Embryo retained within tissues of female parent. The parental tissues provide the developing embryo with nutrients.
Maternal tissue
Land plants are also known as EMBRYOPHYTES
Embryo and placental transfer cell of Marchantia
Wall ingrowths
Placental transfer cell

8. Fossilized spores and tissues
Have been extracted from 475-million-year-old rocks
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.

9. Diversity of Modern Plants
Land plants can be informally grouped based on the presence or absence of vascular tissue

10. An overview of land plant evolution
Land plants
Vascular plants
Bryophytes
(nonvascular plants)
Seedless vascular plants
Seed plants
Mosses
Liverworts
Hornworts
Charophyceans
Gymnosperms
Angiosperms
Pterophyte
(ferns, horsetails, whisk fern)
Origin of seed plants
(about 360 mya)
Lycophytes
(club mosses, spike mosses, quillworts)
Origin of vascular
plants (about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga

11. Bryophytes
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

12. Bryophytes…the video clip
Plant Classifications: Bryophytes." Online . Encyclopædia Britannica Online. 14  Jan.  2008  <

13. Bryophyte Gametophytes
In all three bryophyte phyla
Gametophytes are larger and longer-living than sporophytes

14. Moss Life Cycle…The Movie

15. The life cycle of a moss 4 3 8 6 5 7 1 2 Mature sporophytes
Young sporophyte
Male
gametophyte
Raindrop
Sperm
Key
Haploid (n)
Diploid (2n)
Antheridia
Female gametophyte
Egg
Archegonia
FERTILIZATION
(within archegonium)
Zygote
Archegonium
Embryo
Female gametophytes
Gametophore
Foot
Capsule (sporangium)
Seta
Peristome
Spores
Protonemata
“Bud”
MEIOSIS
Sporangium
Calyptra
Capsule with peristome
Rhizoid
Mature
sporophytes
Spores develop into
threadlike protonemata. 1
The haploid
protonemata
produce “buds”
that grow into
gametophytes. 2
Most mosses have separate
male and female gametophytes,
with antheridia and archegonia,
respectively. 3
A sperm swims
through a film of
moisture to an
archegonium and
fertilizes the egg. 4
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. 8
The sporophyte grows a
long stalk, or seta, that emerges
from the archegonium. 6
The diploid zygote
develops into a
sporophyte embryo within
the archegonium. 5
Attached by its foot, the
sporophyte remains nutritionally
dependent on the gametophyte. 7

16. 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

17. Bryophyte Sporophytes
Grow out of archegonia
Are the smallest and simplest of all extant plant groups
Consist of a foot, a seta (an elongated stalk), and a sporangium
Hornwort and moss sporophytes
Have stomata (like vascular plants) (an opening for gas exchange)

18. Bryophyte diversity LIVERWORTS (PHYLUM HEPATOPHYTA) Gametophore of
HORNWORTS (PHYLUM ANTHOCEROPHYTA)
MOSSES (PHYLUM BRYOPHYTA)
Gametophore of
female gametophyte
Marchantia polymorpha,
a “thalloid” liverwort
Foot
Sporangium
Seta
500 µm
Marchantia sporophyte (LM)
Plagiochila
deltoidea,
a “leafy”
liverwort
An Anthoceros
hornwort species
Sporophyte
Gametophyte
Polytrichum commune,
hairy-cap moss

19. Ecological and Economic Importance of Mosses
Sphagnum, or “peat moss”
Forms extensive deposits of partially decayed organic material known as peat
Peatlands play an important role as carbon reservoirs an help stabilize atmospheric carbon dioxide levels.
(a)
Peat being harvested from a peat bog
Sporangium at
tip of sporophyte
Gametophyte
(b)
Closeup of Sphagnum. Note the “leafy” gametophytes
and their offspring, the sporophytes.
Living
photo-
synthetic
cells
Dead water-
storing cells
100 µm
(c)
Sphagnum “leaf” (LM). The combination of living photosynthetic
cells and dead water-storing cells gives the moss its spongy quality.
(d)
“Tolland Man,” a bog mummy dating from 405–100 B.C.
The acidic, oxygen-poor conditions produced by Sphagnum can preserve human or other animal bodies for thousands of years.

20. Origin and Diversity of Vascular Plants
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 evolve during the Carboniferous period
Fossils of the forerunners of vascular plants date back about 420 million years

21. Seedless Vascular Plants
These early tiny plants
Had branching sporophytes that weren’t dependent on gametopyhtes for growth, but lacked other derived traits of vascular plants
Dichotomous (Y-shaped) branching made possible multiple sporangia. This evolutionary development allowed for greater spore production.
Also increased survival in the face of herbivory. If some sporangia were eaten others might survive.

22. 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

23. Tracheophytes-Pterophyta (ferns) …the video clip
fern." Encyclopædia Britannica Encyclopædia Britannica Online. 13 Jan  <

24. Fern Life Cycle…The Movie

25. The life cycle of a fern Sporangia release spores.
Most fern species produce a single
type of spore that gives rise to a
bisexual gametophyte. 1
The fern spore
develops into a small,
photosynthetic gametophyte. 2
Although this illustration
shows an egg and sperm
from the same gametophyte,
a variety of mechanisms
promote cross-fertilization
between gametophytes. 3
Key
Haploid (n)
Diploid (2n)
Antheridium
Spore
Young
gametophyte
MEIOSIS
Sporangium
Archegonium
Sperm
Mature
sporophyte
Egg
New
sporophyte
Zygote
Sporangium
FERTILIZATION
Sorus
On the underside
of the sporophyte‘s
reproductive leaves
are spots called sori.
Each sorus is a
cluster of sporangia. 6
Fern sperm use flagella
to swim from the antheridia
to eggs in the archegonia. 4
Gametophyte
Fiddlehead
A zygote develops into a new
sporophyte, and the young plant
grows out from an archegonium
of its parent, the gametophyte. 5

26. Transport in Xylem and Phloem
Vascular plants have two types of vascular tissue
Xylem and phloem
Xylem
Conducts most of the water and minerals
Includes dead cells called tracheids. Their cell walls remain to provide the internal ‘pipe system’.
Cell walls are strengthened by the polymer lignin. This allows vascular plants to grow to greater heights than bryophytes
Phloem
Distributes sugars, amino acids, and other organic products
Consists of living cells

27. Evolution of Roots Roots Are organs that anchor vascular plants
Enable vascular plants to absorb water and nutrients from the soil
May have evolved from subterranean stems

28. Evolution of Leaves Leaves Leaves are categorized by two types
Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis
Leaves are categorized by two types
Microphylls, leaves with a single vein
Megaphylls, leaves with a highly branched vascular system

29. Evolution of Leaves According to one model of evolution
Microphylls evolved first, as outgrowths of stems
Vascular tissue
Microphylls may have originated as small stem
outgrowths supported by single, unbranched strands
of vascular tissue.
(a)
Megaphylls, which have branched vascular
systems, may have evolved by the fusion of
branched stems.
(b)

30. Sporophylls and Spore Variations
Are modified leaves with sporangia (may look like a “photosynthetic leaf” may not)
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

31. Classification of Seedless Vascular Plants
Seedless vascular plants form two phyla
Lycophyta, including club mosses, spike mosses, and quillworts. Are small herbaceous plants
Pterophyta, including ferns, horsetails, and whisk ferns and their relatives. Ferns are the most diverse seedless vascular plants

32. Groups of seedless vascular plants
LYCOPHYTES (PHYLUM LYCOPHYTA)
PTEROPHYTES (PHYLUM PTEROPHYTA)
WHISK FERNS AND RELATIVES
HORSETAILS
FERNS
Isoetes
gunnii,
a quillwort
Selaginella apoda,
a spike moss
Diphasiastrum tristachyum, a club moss
Strobili
(clusters of
sporophylls)
Psilotum
nudum,
a whisk
fern
Equisetum
arvense,
field
horsetail
Vegetative stem
Strobilus on
fertile stem
Athyrium
filix-femina,
lady fern

33. Significance of Seedless Vascular Plants
The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Carboniferous, forming the first forests
The growth of these early forests may have helped produce the major global cooling that characterized the end of the Carboniferous period.
They decayed and eventually became coal