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Chapter 28 - SadavaPlants without Seeds: from Water to Land
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Before we start Plants, a review…. Domain Archaea
Prokaryotic, include extremophile bacteria Domain Bacteria
Prokaryotic, includes what we knew as Kingdom Monera
Domain Eukarya Eukaryotic Includes:
Kingdom Fungi What we knew as Kingdom Protista (green algae
are related to plants) Kingdom Plantae Kingdom Animalia
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Land plants are monophyletic all descend from a single
common ancestor One shared derived character
a synapomorphy development from an embryo
protected by tissues of the parent plant Why is this important on land?
Also called embryophytes
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Land plants retain derived features they share with green algae (which are protists): Chlorophyll a and b. Starch as a storage product. Cellulose in cell walls.
Photo 28.2 Green algae of phylum Chlorophyta are most likely ancestors of plants.
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“Plants” can be defined in several ways Streptophytes include land plants and a
paraphyletic group of green algae —all retain egg within parent’s body
Green plants: streptophytes plus all other green algae. All have chlorophyll b
This textbook: “plants” refers only to land plants
What we think of in Kingdom Plantae
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10 clades of land plants
Vascular plants, or tracheophytes 7 clades all have conducting cells called
tracheids
The seven groups of vascular plants constitute a clade themselves
Nonvascular plants 3 clades
www.sonoma.edu/users/c/cannon/
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Plants first appeared on land between 400–500 million years ago
Adaptations were needed to survive in dry environments Large plants must transport water to all
parts of plant Needed support in air Needed methods to disperse gametes
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Characteristics of land plants: The cuticle (waxy lipids) Stomata – openings in stems and leaves;
regulate gas exchange (except liverworts) Gametangia enclosing gametes Embryos in a protective structure Pigments that protect against UV radiation Spore walls containing sporopollenin Mutualistic relationships with fungi to
promote nutrient uptake from soil
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Alternation of generations
All land plants have a life cycle with alternation of generations
multicellular haploid (gametophyte)
multicellular diploid (sporophyte) individuals
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Alternation of generations Sporophyte
Produces spores, all cells are diploid Cells in sporangia (in sporophyte)
undergo meiosis to produce haploid, unicellular spores
Spores are released Spore develops into multicellular haploid
structure, the gametophyte Gametophyte
Produces gametes, all cells are haploid Produce gametes by mitosis Fusion of egg and sperm results in
diploid zygote Zygote develops into sporophyte
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Reduction of the gametophyte generation is a major theme in plant evolution In nonvascular plants: gametophyte is
larger, longer-lived, and more self-sufficient than the sporophyte
Gametophyte is photosynthetic
In plants that appeared later, this is reversed In seed vascular plants (gymnosperms
and angiosperms), sporophyte generation is dominate
Sporophyte is photosynthetic Gametophyte might only be a few cells it is so
small
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Nonvascular plants Do not have vascular tissue liverworts, hornworts, and mosses These groups do not form a clade – why?
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In nonvascular plants, the gametophyte generation is photosynthetic Sporophytes may or
may not be photosynthetic,…
but are always nutritionally dependent on gametophyte, and is permanently attached
http://taggart.glg.msu.edu/bot335/MOSS.GIF
Gametophytes
Sporophytes arising from gametophytes
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Haploid gametophyte produces gametes in specialized sex organs (gametangia) Female: archegonium produces one
egg Male: antheridium produces many
sperm with two flagella each
http://www.dkimages.com/discover/previews/832/20113674.JPG
Flagellated moss sperm Archegonium Antheridium
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• Nonvascular plants• Sperm must swim to
archegonium, or be splashed by raindrops
• Egg or archegonium releases chemical attractants for sperm
• Water is required for all these events
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Vascular Plants• Vascular plants include the club mosses,
ferns, conifers, and angiosperms (flowering plants).
• True roots and leaves
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What Features Distinguish the Vascular Plants?
The vascular system consists of tissue specialized for transport of materials Xylem
conducts water and minerals from soil up to aerial parts of plant.
Some cells have lignin — provides support
Phloem conducts products of photosynthesis
through plant.
http://plantandsoil.unl.edu/croptechnology2005/UserFiles/Image/siteImages/Fig-3-large.gif
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Tracheids are main water-conducting element in xylem
Evolution of tracheids in plants set stage for invasion of land
First plant fossils are from Silurian (408-440 mya) Made land more
hospitable for animals Amphibians and insects
arrived soon after plants
www.unlv.edu/Colleges/Sciences/Biology/Schulte/Anatomy/CellsTissues
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Vascular plants also have a large, branching, independent sporophyte Mature sporophyte is
nutritionally independent from gametophyte
http://web.cortland.edu/broyles/hayghttp://virtual.yosemite.cc.ca.us/randerson/Lynn's%20Bioslides/20.jpg
Small independent gametophyte (left) and branched sporopythe (right) of ferns
Fern prothallus
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• Vascular plants• Euphyllophytes• “true leaf plants”• Includes:• Monilophytes – seedless vascular plants that have
megaphylls • seed plants (gymnosperms and flowering plants)
• Synapomorphies include overtopping growth — new branches grow beyond the others —an advantage in the competition for light
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True leaves evolved flattened photosynthetic structures
arising from a stem or branch has true vascular tissue two types
Microphylls – small, one vascular strand Club mosses have these
Megaphylls
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Heterosporous vascular plants produce two types of spores: Megaspores develop into female
gametophytes — megagametophyte Megaspores are produced in small
numbers in megasporangia Microspores develop into male
gametophytes — microgametophyte Microspores are produced in large
numbers in microsporangia
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Nonvascular seedless land plants: three clades: liverworts mosses hornworts
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EmbryophytesNonvascular Seedless plantsHepatophyta
Liverworts: Hepatophyta Sporophytes very short
Remember that gametophyte generation is dominant in nonvascular plants
Can reproduce asexually Do so by dispersing gemmae which are in
gemmae cups
www.bcbiodiversity.homestead.com/files
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EmbryophytesNonvascular Seedless plantsBryophyta
The mosses: Bryophyta Mosses (plus hornworts and vascular
plants) have stomata important in water & gas exchange
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EmbryophytesNonvascular Seedless plantsAnthocerophyta
Hornworts: Anthocerophyta Gametophytes are flat plates of cells Have stomata, which do not close
http://www.botany.org/PlantImages/Conant/CA06-014_300.jpg
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Seedless Vascular Plants
Seedless VASCULAR plants – three monophyletic clades: club mosses horsetails whisk ferns
plus ferns and allies (not monophyletic, though 97% are)
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Seedless Vascular Plants
Seedless vascular plants Small, short-lived
gametophyte is independent of the large sporophyte
Single-celled spore is resting stage
Can grow larger because of vascular tissue but must have water for part of life cycle — for the flagellated, swimming spermwww.biologie.uni-hamburg.de/b-online/library/webb/BOT311/FERNS
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EmbryophytesSeedless Vascular PlantsLycophytes
Lycophytes: club mosses, spike mosses, and quillworts Roots and stems have dichotomous
branching Leaves are microphylls Strobilli – clusters of sporangia
Lycopodium annotinum
http://ip30.eti.uva.nl/bis/flora/pictures
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EmbryophytesSeedless VascularEuphyllophytesMonilophytes
Monilophytes (a.k.a. Pteridophytes) — horsetails, whisk ferns, and ferns & allies, form a clade Horsetails and whisk ferns are both
monophyletic, but ferns are not But 97% of ferns form a clade — the
leptosporangiate ferns
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EmbryophytesSeedless VascularEuphyllophytesMonilophytes
Horsetails 15 species in one
genus — Equisetum Silica in cell walls —
“scouring rushes”… used for cleaning
www.plantoftheweek.org/image
Equisetum hymale
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EmbryophytesSeedless VascularEuphyllophytesMonilophytes
Whisk ferns 15 species in two
genera No roots but
well-developed vascular system
http://www.botanik.uni-karlsruhe.de/garten/fotos-knoch/Psilotum%20nudum%20Gabelblatt%201.jpg
Psilotum nudum
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EmbryophytesSeedless VascularEuphyllophytesMonilophytes
Sporangia occur on undersides of leaves in clusters called sori
http://departments.bloomu.edu/biology/pics/botany/fern_sori2w.jpg
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Monilophytes (Pteridophytes) – Ferns
Fern gametophytes produce antheridia and archegonia, not always at same time or on same gametophyte
www.esu.edu/~milewski/intro_biol_two/lab_2_moss_ferns
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EmbryophytesSeedless VascularEuphyllophytesMonilophytes
Most ferns found in shaded, moist environments Tree ferns can reach heights of 20 m
http://www.we-du.com/images/plants/350/frndrydwf.jpg
Dixie Woods fern, Dryopteris australis
Tree fernshttp://www.wettropics.gov.au/st/rainforest_explorer/Resources/Images/plants/TreeFerns.jpg