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Seedless PlantsChapter 30
Origin of Land Plants
• All green algae and the land plants shared a common ancestor a little over 1 BYA– Kingdom Viridiplantae – Not all photoautotrophs are plants
• Red and brown algae are excluded
• A single species of freshwater green algae gave rise to the entire terrestrial plant lineage
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• 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
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Ancestral alga
Chlorophytes Charophytes Liverworts HornwortsMosses Lycophytes Gymnosperms Angiosperms
Seed plantsEuphyllophytes
Bryophytes
Land plantsStreptophyta
Green plants
Green algaeGreen algae
Red Algae
Tracheophytes
Ferns + Allies
• Adaptations to terrestrial life – Protection from desiccation
• Waxy cuticle and stomata
– Moving water using tracheids• Tracheophytes have tracheids
– Xylem and phloem to conduct water and food
– Dealing with UV radiation caused mutations• Shift to a dominant diploid generation
– Haplodiplontic life cycle• Mulitcellular haploid and diploid life stages• Humans are diplontic
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Haplodiplontic Life Cycle
• Multicellular diploid 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
• Multicellular haploid stage – gametophyte– Spores divide by mitosis
– Produces gametes by mitosis
– Gametes fuse to form diploid zygote• First cell of next sporophyte generation
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Spore
Spore
n
n
nn
Spore mother cell
2n
Sporangia
Sporophyte(2n)
2n
2n Zygote
Embryo
Egg
Sperm
MEIOSIS
MITOSIS
FERTILIZATION
n
2n
Gametophyte(n)
• All land plants are haplodiplontic
• Relative sizes of generations vary
• Moss– Large gametophyte– Small, dependent sporophyte
• Angiosperm– Small, dependent gametophyte– Large sporophyte
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Bryophytes
• Closest living descendants of the first land plants
• Called nontracheophytes because they lack tracheids– Do have other conducting cells
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• Mycorrhizal associations important in enhancing water uptake– Symbiotic relationship between fungi and
plants
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ch
aro
ph
yte
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Liv
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Mo
ss
es
Ho
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Tra
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• Simple, but highly adapted to diverse terrestrial environments
• 24,700 species in 3 clades– Liverworts– Mosses– Hornworts
• Gametophyte – conspicuous and photosynthetic– Sporophytes – small and dependent
• Require water for sexual reproduction
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Liverworts (phylum Hepaticophyta)
• Have flattened gametophytes with liverlike lobes– 80% look like mosses
• Form gametangia in umbrella-shaped structures
• Also undergo asexual reproduction
Femalegametophyte
© David Sieren/Visuals Unlimited
Leafy vs Thallose Liverworts
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Leafy vs Thallose Liverwort
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Marchantia polymorpha
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Liverwort Sex…(if you are under 18, please close your eyes!)
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Click here for XXX rated liverwort porn
MossesMoss grows on the north side of a tree…
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“Haircap Moss”, Polytrichum
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Hair Cap Moss
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Apple Moss, Bartramia
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Pin Cushion Moss, Leucobryum
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Delicate Fern Moss, Thuidium
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Mosses (phylum Bryophyta)
• Gametophytes consist of small, leaflike structures around a stemlike axis– Not true leaves – no vascular tissue
• Anchored to substrate by rhizoids• Multicellular gametangia form at the tips of
gametophytes– Archegonia – Female gametangia– Antheridia – Male gametangia
• Flagellated sperm must swim in water
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Sporophyte
Gametophyte
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
n
2n
2n
2n
1n
1n
Sperm
Sporangium
Antheridia
Egg
Archegonia
Gametophytes
Spores
Rhizoids
Female
Male
Zygote
MITOSIS
FERTILIZATION
Maturesporophyte
Developingsporophyte inarchegonium
Parentgametophyte
MITOSIS
MIE
IOSIS
Germinatingspores
Hornworts (phylum Anthocerotophyta)• Origin is puzzling – no fossils until Cretaceous• Sporophyte is photosynthetic• Sporophyte embedded in gametophyte tissue• Cells have a single large chloroplast
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Photosyntheticsporophyte
Tracheophyte Plants
• Cooksonia, the first vascular land plant– Appeared about 420 MYA– Phylum Rhyniophyta
• Only a few centimeters tall– No roots or leaves– Homosporous – only 1 type of
spore
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Sporangia
Vascular tissues
• Xylem– Conducts water and dissolved minerals upward from
the roots
• Phloem– Conducts sucrose and hormones throughout the plant
• Enable enhanced height and size in the tracheophytes
• Develops in sporophyte but not gametophyte• Cuticle and stomata also found in land plants
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Tracheophytes
• Vascular plants include seven extant phyla grouped in three clades1. Lycophytes (club mosses)
2. Pterophytes (ferns, whisk ferns, and horsetails)
3. Seed plants
• Gametophyte has been reduced in size relative to the sporophyte during the evolution of tracheophytes
• Similar reduction in multicellular gametangia has occurred as well
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• Stems– Early fossils reveal stems but no roots or leaves– Lack of roots limited early tracheophytes
• Roots– Provide transport and support– Lycophytes diverged before true roots appeared
• Leaves– Increase surface area for photosynthesis– Evolved twice
• Euphylls (true leaves) found in ferns and seed plants• Lycophylls found in seed plants
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Euphyll Origins
Lycophyll Origins
Stem withvascular tissue
Stem, leafy tissuewithout vascular tissue
Stem, leafy tissuewith vascular tissue
Singlevascular strand
(vein)
Branchedvascular strands
(veins)Photosynthetic tissue
“webs” branchesBranches in
single planesUnequal
branchingBranching stems
with vascular tissue
• 400 million years between appearance of vascular tissue and true leaves– Natural selection favored plants with higher stomatal
densities in low-CO2 atmosphere
– Higher stomatal densities favored larger leaves with a photosynthetic advantage that did not overheat
• Seeds– Highly resistant– Contain food supply for young plant– Lycophytes and pterophytes do not have seeds
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• Fruits in the flowering plants (angiosperms) add a layer of protection to seeds and attract animals that assist in seed dispersal, expanding the potential range of the species
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Ancestral alga
Chlorophytes Charophytes Liverworts HornwortsMosses Lycophytes Gymnosperms Angiosperms
Chlorophyll a and bPlasmodesmata
CuticleAntheridia and archegoniaMulticellular embryo
Stomata
EuphyllsSeeds
FlowersFruits
Dominant sporophyteStems, roots, leaves
Ferns + Allies
Vascular tissue
Lycophytes
• Worldwide distribution – abundant in tropics• Lack seeds• Superficially resemble true mosses• Sporophyte dominant• 15 PA species 36
Ho
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Lyc
op
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See
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Fer
ns
and
Alli
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Princess PineDendrolycopodium
obscurum
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Shining Club MossLycopodium lucidulum
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39Ground Pine
Pterophytes
• 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
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Lyc
op
hyt
es
Fer
ns
Ho
rset
ail F
ern
s
Fer
ns
Wh
isk
Fer
ns
See
d P
lan
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Whisk Ferns• Found in tropics, none locally• Sporophyte consists of evenly
forking green stems without true leaves or roots (found to be monophyletic with ferns)
• Some gametophytes develop elements of vascular tissue– Only gametophytes known to do
so
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Horsetails• All 15 living species are
homosporous• Constitute a single genus,
Equisetum; 5 species in PA• Sporophyte consists of ribbed,
jointed photosynthetic stems that arise from branching rhizomes with roots at nodes
• Silica deposits in cells – scouring rush
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Ferns
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
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• Fern life cycle differs from that of a moss
• Much greater development, independence, and dominance of the fern’s sporophyte
• Gametophyte lacks vascular tissue
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MEIOSIS
n
2n
Archegonium
Archegonium
Antheridium
Antheridium
Egg
Sperm
Embryo
1n
Gametophyte
Rhizome
Sporangium
Spores
Rhizoids
Gametophyte
MITOSIS
Undersideof leaf frond
Maturesporangium
Sorus (clusterof sporangia)
Adultsporophyte
Maturefrond
Leaf of youngsporophyte
MITOSIS
Zygote2n
FERTILIZATION
• Fern morphology– Sporophytes have rhizomes– Fronds (leaves) develop at the tip of the rhizome as
tightly rolled-up coils (“fiddleheads”)46
Tightly Coiled Fern Uncoiling Fern
(left): © Mike Zens/Corbis; (right): © Ed Reschke
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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
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rhizome
fiddlehead/crozier
sterile frondfertile frond
Ferns
Pinnate Pinnatifid
Not everything
that looks like a fern is one!
…and not everything that is a fern looks
like one!
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Ostrich FernMatteuccia struthiopteris
•separate fertile and vegetative fronds
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Sensitive FernOnoclea sensibilis
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Hay-scented FernDennstaedtia punctilobula
