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Seedless Plants
Chapter 30
Origin of Land Plants
• All green algae and the land plants shared a
common ancestor a little over 1 BYA
– Kingdom Viridiplantae (green plants)
– Not all photoautotrophs are plants
• Red and brown algae excluded
– A single species of freshwater green algae gave rise to
the entire terrestrial plant lineage
Green plants
Streptophyta
Land plants
Bryophytes
Green algae
Green algae
Red Algae Chlorophytes Charophytes Liverworts Mosses
Tracheophytes
Euphyllophytes
Seed plants
Hornworts Lycophytes Ferns + Allies Gymnosperms Angiosperms
2
Ancestral alga
• The green algae split into two major clades
– Chlorophytes – Never made it to land
– Charophytes – Sister to all land plants
• Land plants …
– Have multicellular haploid and diploid stages
– Trend toward more diploid embryo protection
– Trend toward smaller haploid stage
Green plants
Streptophyta
Land plants
Bryophytes
Tracheophytes
Euphyllophytes
Red Algae
Green algae
Green algae
Chlorophytes
Charophytes
Seed plants
Liverworts
Mosses
Hornworts
Lycophytes
Ferns + Allies
Gymnosperms
Angiosperms
3
Ancestral alga
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Green plants
Streptophyta
Land plants
Bryophytes
Tracheophytes
Euphyllophytes
Red Algae
Green algae
Green algae
Chlorophytes
Charophytes
Seed plants
Liverworts
Mosses
Hornworts
Lycophytes
Ferns + Allies
Gymnosperms
Angiosperms
Ancestral alga
4
• Adaptations to terrestrial life
– Moving water using tracheids
• Tracheophytes (vascular plants) have
tracheids
– Xylem and phloem to conduct water and food
Pine xylem
(tracheids) and
phloem
6
http://faculty.unlv.edu/schulte/Anatomy/CellsTissues/Cells.html
http://en.wikipedia.org/wiki/Pyrimidine_dimer
• Adaptations to terrestrial life
– Dealing with UV radiation-caused
mutations
• Shift from dominant haploid to a
dominant diploid generation
• Diploid form allows redundancy of
alleles to mask mutations
– Haplodiplontic life cycle
• “Alternation of generations”
• Mulitcellular haploid (gametophyte)
and diploid (sporophyte) life stages
• Humans are diplontic; fungi haplontic
7
Haplodiplontic Life Cycle
• Things to remember
–
–
–
–
Spores are haploid
Gametes are haploid
Zygotes are diploid
Mieosis: 2n  1n
Gametophyte
(n)
MITOSIS
Spore
n
n
Sperm
n
n Spore
MEIOSIS
Egg
n
FERTILIZATION
2n
2n Spore mother
cell
2n
Zygote
2n
Sporangia
Embryo
Sporophyte
(2n)
8
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect19.htm
Haplodiplontic Life Cycle
• Multicellular diploid (2n)
stage – sporophyte
– Produces haploid
spores by meiosis
– Diploid spore mother
cells (sporocytes)
undergo meiosis in
sporangia
• Produce 4 haploid spores
• First cells of gametophyte
generation
Gametophyte
(n)
MITOSIS
Spore
n
n
Sperm
n
n Spore
MEIOSIS
Egg
n
FERTILIZATION
2n
2n Spore mother
cell
2n
Zygote
2n
Sporangia
Embryo
Sporophyte
(2n)
9
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect19.htm
Haplodiplontic Life Cycle
• Multicellular haploid (1n)
stage – gametophyte
– Spores divide by mitosis
– Produces gametes by
mitosis
– Gametes fuse to form
diploid zygote
• First cell of next
sporophyte generation
Gametophyte
(n)
MITOSIS
Spore
n
n
Sperm
n
n Spore
MEIOSIS
Egg
n
FERTILIZATION
2n
2n Spore mother
cell
2n
Zygote
2n
Sporangia
Embryo
Sporophyte
(2n)
10
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect19.htm
http://www.biologie.uni-hamburg.de/b-online/library/webb/BOT311/Mosses/SexRepro-1.htm
• All land plants are
haplodiplontic
• Relative sizes of generations
vary  evolutionary trend
– Mosses
• Large gametophyte
• Small, dependent sporophyte
– Ferns  intermediate
– Gymnosperms & Angiosperms
• Small, dependent gametophyte
• Large sporophyte
11
http://biologytb.net23.net/text/chapter19/concept19.5.html
http://mycorrhizas.info/method.html
“Bryophytes”
– Do have other conducting cells
• Mycorrhizal associations
enhance water uptake
12
– Symbiotic relationship between
fungi and plants
Tracheophytes
Hornworts
Mosses
Liverworts
• Closest living descendants of
the first land plants
• Called nontracheophytes
(“non-vascular” plants)
because they lack tracheids
Charophytes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Tracheophytes
Hornworts
Mosses
Liverworts
– Liverworts
– Mosses
– Hornworts
Charophytes
• 24,700 species in 3 clades
• Simple, but highly adapted to
diverse terrestrial environments
• Gametophyte – conspicuous and
photosynthetic
– Sporophytes – small and dependent
• All require water for sexual
reproduction
13
http://www.biologie.uni-hamburg.de/b-online/library/webb/BOT311/Mosses/SexRepro-1.htm
Liverworts (phylum Hepaticophyta)
• Have flattened
gametophytes with
liverlike lobes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Female
gametophyte
– 80% look like mosses
• Form gametangia in
umbrella-shaped
structures
• Also undergo asexual
reproduction
© David Sieren/Visuals Unlimited
14
http://palaeos.com/plants/bryophyta/bryophyta.html
Mosses (phylum Bryophyta)
• Gametophytes consist of
small, leaflike structures
around a stemlike axis
– Not true leaves – no
vascular tissue
• Anchored to substrate by
rhizoids
– Not true roots – no
vascular tissue
15
http://www.bluetier.org/liverwort2/hornwort-4.JPG
Hornworts (phylum Anthocerotophyta)
• Origin is puzzling – no fossils until Cretaceous
• Sporophyte is photosynthetic
– Sporophyte embedded in gametophyte tissue
• Cells have a single large chloroplast
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Photosynthetic
sporophyte
18
© Lee W. Wilcox
Tracheophyte
(Vascular) Plants
• Cooksonia, the first vascular
land plant
– Appeared about 420 MYA
– Phylum Rhyniophyta (extinct)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sporangia
• Only a few centimeters tall
– No roots or leaves
– Homosporous – only 1 type of
spore
19
Vascular tissues
• Xylem
– Conducts water and dissolved
minerals upward from the roots
• Phloem
– Conducts sucrose and
hormones throughout plant
20
http://faculty.unlv.edu/schulte/Anatomy/CellsTissues/Cells.html
http://2pat.wordpress.com/category/plantstrees/
Vascular tissues
• Vascular tissues enable enhanced height & size in
tracheophytes
– Develops in sporophyte but not gametophyte (reason
sporophytes dominate in most vascular plants)
– Cuticle & stomata also found in tracheophytes
The giant redwood (Sequoia
sempervirens) is the tallest species
on Earth, up to 115.5 m (379 ft).
21
http://www.daviddarling.info/encyclopedia/A/alternation_of_generations.html
Tracheophytes
• Major evolutionary trend: Gametophyte has been
reduced in size relative to the sporophyte during
the evolution of tracheophytes
– Similar reduction in multicellular gametangia has
occurred as well
22
http://www.sciencedirect.com/science/article/pii/S0959437X08000683
Tracheophytes
• Vascular plants
include seven extant
phyla grouped in
three clades
1. Lycophytes (club
mosses)
2. Pterophytes (ferns,
whisk ferns, and
horsetails)
3. Seed plants
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24
http://www.geol.umd.edu/~tholtz/G204/lectures/204green.html
Tracheophytes
• Stems
Fossil lycophyte
(Baaragwanathia sp.)
– Early fossils reveal stems but
no roots or leaves
– Lack of roots limited early
tracheophytes
• Roots
– Provide transport, support, anchorage
– Lycophytes diverged before true roots
appeared (independently arose in
lycophytes and other tracheophytes)
25
• Leaves
– Increase surface area for photosynthesis
– Evolved twice
• Lycophylls (microphylls) found in lycophytes (club mosses)
• Euphylls (true leaves) found in ferns & seed plants
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lycophyll Origins
Stem with
vascular tissue
Stem, leafy tissue
without vascular tissue
Stem, leafy tissue
with vascular tissue
Single
vascular strand
(vein)
Euphyll Origins
Branching stems
Unequal
with vascular tissue branching
Branches in Photosynthetic tissue
single planes
“webs” branches
Branched
vascular strands
(veins)
26
http://commons.wikimedia.org/wiki/File:Selaginella_uncinata_002_%28%E5%A4%A9%E5%95%8F%29.jpg
• 400 million years between appearance of vascular
tissue and true leaves
– Natural selection favored plants with higher stomatal
densities & active stomatal control in low-CO2
atmosphere (figures below for extant lycophyte,
Selaginella uncinata)
– Higher stomatal densities favored larger leaves with a
photosynthetic advantage that did not overheat
27
http://www.sciencedirect.com/science/article/pii/S0960982211004866
http://upcard.in/Alltypesofseeds.aspx
• Seeds
–
–
–
–
Highly resistant
Contain food supply for young plant
Many modes of dispersal
Major innovation in seed plants (gymosperms &
angiosperms) Lycophytes and pterophytes do not have
seeds
28
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chlorophytes
Charophytes
Liverworts
Mosses
Hornworts
Lycophytes
Ferns + Allies
Gymnosperms
Angiosperms
Flowers
Fruits
Seeds
Euphylls
Stems, roots, leaves
Dominant sporophyte
Vascular tissue
Stomata
Multicellular embryo
Antheridia and archegonia
Cuticle
Plasmodesmata
Chlorophyll a and b
Ancestral alga
• Fruits in the flowering plants (angiosperms)
– Add a layer of protection to seeds
– Attract animals that assist in seed dispersal,
expanding the potential range of the species
29
• Worldwide distribution –
abundant in tropics
• Lack seeds
• Superficially resemble true
mosses
• Sporophyte dominant
30
Seed Plants
Ferns and Allies
Lycophytes
Lycophytes
Hornworts
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Seed Plants
Whisk Ferns
Ferns
Horsetail Ferns
• Phylogenetic
relationships among
ferns and their relatives
is still being sorted out
• Common ancestor gave
rise to 2 clades
• All form antheridia and
archegonia
• All require free water for
flagellated sperm
Ferns
Pterophytes
Lycophytes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
31
http://faculty.fmcc.suny.edu/mcdarby/animals&plantsbook/Plants/03-Ferns.htm
Whisk ferns
• Found in tropics
• Sporophyte consists of
evenly forking green stems
without true leaves or roots
• Some gametophytes
develop elements of
vascular tissue
– Only one known to do so
32
Horsetails
• All 15 living species are
homosporous
• Constitute a single species,
Equisetum
• Sporophyte consists of ribbed,
jointed photosynthetic stems
that arise from branching
rhizomes with roots at nodes
• Silica deposits in cells –
scouring rush
33
Ferns
• Most abundant group of
seedless vascular plants
– About 11,000 species
• Coal formed from forests 300
MYA
• Conspicuous sporophyte and
much smaller gametophyte are
both photosynthetic
Fern gametophyte
spouting a sporophyte
(vertical sprout)
34
http://en.wikipedia.org/wiki/Alternation_of_generations
Fern life cycle
differs from that of
a moss
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Antheridium
Archegonium
Rhizoids
Archegonium
Egg
Sperm
Gametophyte
MITOSIS
Antheridium
Spores
1n
MEIOSIS
Zygote
2n
n
MITOSIS
2n
Underside
of leaf frond
Mature
frond
Leaf of young
sporophyte
Adult
sporophyte
Mature
sporangium
Embryo
• Much greater
development,
independence, and
dominance of the
fern’s sporophyte
• Gametophyte lacks
vascular tissue
Sorus (cluster
of sporangia)
Gametophyte
Sporangium
Rhizome
35
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Tightly Coiled Fern
Uncoiling Fern
(left): © Mike Zens/Corbis; (right): © Ed Reschke
• Fern morphology
– Sporophytes have rhizomes
– Fronds (leaves) develop at the tip of the rhizome as
tightly rolled-up coils (“fiddleheads”)
36
http://www.proprofs.com/flashcards/story.php?title=nonvascular-vascular-plantsbiology-112
Fern reproduction
• Produce distinctive sporangia in
clusters called sori on the
back of the fronds
• Diploid spore mother cells in
sporangia produce haploid
spores by meiosis
• Spores germinate into
gametophyte
– Rhizoids but not true roots – no
vascular tissue
• Flagellated sperm, require water
37
http://palaeos.com/plants/glossary/glossarySi.html