1. This is a presentation used during
Botany lecture on nonvascular
plants.
To complete the entire lecture would be about 2 lectures. When
questions are stated in the presentation, usually students get
into groups to discuss, then we will have a general class
discussion on the question and at the end of the lecture an
activity sheet was given as review
Charleen Baker

2. Chapter 20
Nonvascular Plants: Mosses,
Liverworts, and Hornworts

3. Review of Terms
• Meiosis occurs at some point for organisms that reproduce
sexually
• When gametes unite forming a zygote which has 2 complete
sets of chromosomes
• A cell with one set of chromosomes – haploid
• A cell with two sets of chromosomes – diploid
• End of meiosis – 4 haploid cells produced from 1 diploid cell

4. • Many plants contain more than 2 sets of chromosomes & called
polyploidy
• 3 sets of chromosomes – Triploid – ex) navel oranges &
seedless watermelons – gametes are not inviable & no seeds
produced
• Bread wheat – hexaploid (6 sets)
• Strawberry – octaploid (8 sets)

5. Alternation of Generations
• In animals – only haploid cells have single set of chromosomes -
called gametes (egg & sperm), Generally this is not true in plants
• Complete life cycle of a diploid species that undergoes sexual
reproduction there is an alternation between sporophyte (2n,
diploid) and haploid gametophyte (n) phase
• This is a called Alternation of Generations
• 2n – refers to sporophyte generation or the stages in the life
cycle produced by fertilization
• 1n – refers to the gametophyte generation or stages in the life
cycle produced by meiosis

6. • Diploid body – sporophyte
• Develops from a zygote
• Eventually produces sporocytes which each undergoes meiosis &
produces a spore
• Haploid body – gametophyte
• Develops from a mitotic divisions of spores produced by the
sporophyte
• Specialized cells within gametophytes function as gametes

7. Six rules for Alternation of Generation
1. First cell of the
gametophyte generation is
a spore & the last cell is a
gamete
2. Any cell of the
gametophyte generation
(n) contains half as many
chromosomes as the
sporophyte generation

8. 3. First cell of the sporophyte
generation is a zygote and the last
cell is a spore
4. Any cell of sporophyte generation
(2n) contains twice as many
chromosomes as the gametophyte
generation
5. Change from sporophyte to
gametophyte generation occurs as
a result of meiosis
6. Change from gametophyte to
sporophyte generation occurs as a
result of fusion of gametes at
fertilization

9. Advantages and Disadvantages of
Alternation of Generation
Think, Discuss and Share

10. 3 Groups
of Plants
• Have neither vascular
tissues nor seeds, the
non-vascular plants
(often called
“bryophytes”)
• Have vascular tissue
but not seeds, the
vascular cryptogams
• Have both vascular
tissue and seeds,
spermatophytes

11. Objectives for NonVascular Plants
• Describe structural
adaptations for
moving to land
• Explain their
alternation of
generation
• Compare mosses,
liverwort & hornwort
• Ecological &
Economic
Importance

12. List some of the problems
associated with a terrestrial
environment
How can these problems be
solved by plants?

13. Characteristics of Nonvascular Plants
• World War I – nurses used green material found by a lake as a
bandage – which was much better than cotton bandages
• It was Sphagnum moss – which has antiseptic properties, has
specialized water absorbing leaves & used as packing material
• One of about 23,000 species of bryophytes
• Ex) moss, liverworts & hornworts

14. • Some can withstand long periods of desiccation – found on bare
rocks
• Others occur on frozen alpine slopes
• Habitats range from sea level up to 5,500 or more meters in
mountains
• Some highly restricted and other not in their habitat

15. • Often have mycorrhizal fungi associated with their rhizoids
• Widespread peat moss are ecologically very important in bogs &
transformation of bogs to dry land
• Peat moss can form a mat over water & keep conditions acidic
inhibit other growth so many organisms can be preserved in
bogs

16. • None have true xylem or phloem
• To be able to sexually reproduce must have external water
usually in the form of dew or rain
• Many have special water & mineral conducting cells called
hydroids in the center of the stems
• Few have food conducting cells called leptoids surrounding the
hydroids
• Neither conduct efficiently, most absorb directly though the
surface

17. • Bryophytes are soft & pliable
• Birds use them for their nests
• Leafy plant is the major part –
gametophyte generation
produces gametes
• Sporophyte generation – which
grows from leafy gametophyte
produces spores
• Being embryophytes, they have
multicellular sporangia and
gametangia
alternation of heteromorphic
generations

18. • Nonvascular plants are almost exclusively terrestrial and have a
cuticle over much of their bodies, and many have stomata
• Nonvascular plants can never grow to be really large, but being
small & simple provides great selective advantage in certain
habitats
• All bryophytes have similar life cycles & growth habits however
based on their structure & reproduction they are separated into 3
groups

19. MOSSES
Division - Bryophyta

20. General Characteristics of Mosses
• Gametophyte – plant you see the
most
• “Leaves” – have no mesophyll
tissue, stomata or veins
• Blades usually 1 cell thick,
except midrib
• No petiole
• Contains numerous lens shaped
chloroplasts

21. • Axis is somewhat stem like but no
xylem or phloem
• Base – root like rhizoids consisting
of several rows of colorless cells that
anchor the plant
• All moss stems have leaves, but
because they are parts of a
gametophyte, not a sporophyte, they
are not homologous with those of
vascular plants

22. • Moss gametophytes are both large and
photosynthetic, and they support the
sporophyte throughout its entire life
• All moss sporophytes form from the
zygote and have 3 basic components at
maturity: foot, capsule (where spores
are produced), and seta
• None is ever branched or has leaves,
bracts, or buds of any kind

23. • Certain mosses can grow on hard, impervious surfaces because
they have no roots that must penetrate the substrate
• The majority of mosses lack hydroids and leptoids; water is
conducted along the exterior of their stems by capillary action
• Some water absorbed by rhizoids rises up the central strand
• Closely packed habit & they rarely extend more than a few
centimeters into the air, favors such water movement
• Water absorbed directly through the plant surfaces

24. Always a welcome sight, the White Water-lily
attracts us (and a wide variety of insects) with
its perfumed scent, as well.This very common
herbaceous plant can be found throughout the
Pinelands, and is one of the most noticeable of
all the aquatic plants, even when not flowering.
The flat “lily pads” floating on the surface
appear fresh and delicate when they first
emerge. They provide food for a variety of
creatures and finally disappear as winter
comes along. But the plants are perennial, so
those that live through the winter send new
shoots to the surface each spring, and the
seeds that germinate create new plants.
Duration: Perennial
Flower: early June to late September.
Habitat: ponds, cranberry reservoirs, streams.
White Water-lily
Nymphaea odorata
subsp. odorata

25. List some of the problems
associated with a terrestrial
environment
How can these problems be
solved by plants?

26. Division Bryophyta: Life Cycle

27. • Gametophyte generation
forms when haploid spore
germinates & produces a
protonema filament
• From protonema, shoots
(gametophytes) arise

28. • Gametophytes produce male & female gametangia – often on
the same plant but can be on separate plants
• Archegonia – Female gametangia) – cylindrical & project
upward from the base of extended gametophyte tip
• Single egg produced in cavity

29. • Antheridia (male gametangia) – walls 1 cell thick
• Borne on short stalks
• Sperm forced out of the top of the Antheridium when it absorbs
water & swells
• Each sperm has flagella

30. • Secretion of sucrose from the archegonia guides sperm as they
swim toward the archegonia and then to the egg, where one
sperm cell effects fertilization & a zygote is formed
• Embryo breaks down archegonium & becomes attached to the
stem by a swollen knob called the foot
• It grows & when it breaks through the top of the venter it is a
sporophyte
• Sporophyte is first photosynthetic but is still dependent on the
gametophyte
• When mature, capsule opens and releases haploid spores

31. Asexual Reproduction
• May occur by fragmentation or gemmae
• Pieces of gametophyte can break off & form new plants
• Gemmae are tiny, cup shaped structures on the gametophyte
• Raindrops separate gemmae from the parent so it spreads them
out

32. Metabolism and Ecology
• The small size and lack of conducting tissues are two critical
factors in the metabolism and ecology of mosses
• Without vascular tissue, stems and leaves can become
desiccated, even while the rhizoids are in contact with moist soil
or tree bark
• Several mechanisms compensate for the inability of mosses to
retain water, such as life in moist habitats

33. Liverworts
Division - Hepatophyta

34. General Characteristics of Liverworts
• Small plants that have an alternation of heteromorphic
generations
• The sporophyte is even less conspicuous than in mosses and is
also completely dependent on the gametophyte
• About 8000 species
• Types – Leaflike or Thalloid

35. • Liverwort gametophores may be either bisexual, producing
both antheridia and archegonia, or unisexual, depending on
the species

38. Hornworts
Division - Anthocerophyta

39. General Characteristics of Hornworts
• Leafy like liverworts
• Archegonia & antheridia form inside the plant
• After fertilization, zygotes develop into long, horn shaped
sporophytes
• Sporophytes capable of photosynthesis

40. • Hornworts are a group of small, inconspicuous thalloid plants
that grow on moist soil, hidden by grasses and other herbs
• Hornworts superficially resemble thalloid liverworts, but never
contain oil bodies
• One of the most striking features is the presence of a single
large chloroplast in each cell as opposed to the numerous small
plastids present in all other nonalgal plants

41. Ecological Importance
• Pioneers of bare rock
• Can retain water (especially mosses)
• Reduce flooding & erosion
• Peat moss – packing, acidity, soil conditioner & as a fuel

42. Summary
• They evolved to survive the occasional drying of their streams,
small lakes and ocean-mud flats.
• One strategy for surviving temporary dry spells was the
evolution of drought-resistant spores.
• Large, compact, multicellular body retains water better than
small unicellular or filamentous bodies.
• Water-proofing cuticle would be advantageous
• Coordination of gamete production with moisture for swimming
sperm

43. • Due to dry land conditions, gamete and spore mother cells
needed protection from dryness
• Such reproductive modifications resulted in the grouping and
protection of spore and gamete mother cells into the
sporangia and gametangia characteristic of all embryophytes
—more massive than those of algae and protected by a layer
of sterile cells.

44. Most mosses do not retain water
well. What adaptations have evolved
to permit them to inhabit terrestrial
areas?

45. Next Steps!
• As a truly terrestrial existence became more successful, the
environment became selective for mutations that produced an
upright body that could grow into brighter light.
• Production of pollen and seeds eliminates the need for
environmental water for reproduction
• Vascular tissue, especially phloem, also made feasible the
evolution of truly heterotrophic tissues—roots, meristems, and
organ primordia