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Seedless Plants Chapter 30
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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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Green plants Streptophyta Land plants Bryophytes Tracheophytes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Green plants Streptophyta Land plants Bryophytes Tracheophytes Euphyllophytes Green algae Green algae Seed plants Red Algae Chlorophytes Charophytes Liverworts Mosses Hornworts Lycophytes Ferns + Allies Gymnosperms Angiosperms Ancestral alga
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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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n 2n MITOSIS MEIOSIS FERTILIZATION Gametophyte (n) Spore Sperm n n Egg
Spore mother cell 2n Zygote Sporangia 2n Embryo Sporophyte (2n)
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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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Closest living descendants of the first land plants Called nontracheophytes because they lack tracheids Do have other conducting cells Charophytes Tracheophytes Liverworts Hornworts Mosses Mycorrhizal associations important in enhancing water uptake Symbiotic relationship between fungi and plants
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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 Female gametophyte © David Sieren/Visuals Unlimited
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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!)
Click here for XXX rated liverwort porn
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Moss grows on the north side of a tree…
Mosses Moss 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 Male Gametophytes Sperm Egg Antheridia
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Male Gametophytes Sperm Egg Antheridia Archegonia FERTILIZATION Female Germinating spores Rhizoids Sporophyte Zygote n 2n MITOSIS MITOSIS Gametophyte Spores Mature sporophyte 2n 1n MIEIOSIS Developing sporophyte in archegonium 2n Sporangium Parent gametophyte 1n
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Hornworts (phylum Anthocerotophyta)
Origin is puzzling – no fossils until Cretaceous Sporophyte is photosynthetic Sporophyte embedded in gametophyte tissue Cells have a single large chloroplast Photosynthetic sporophyte
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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 Sporangia
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Vascular tissues Xylem Phloem
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 clades Lycophytes (club mosses) Pterophytes (ferns, whisk ferns, and horsetails) 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 Roots Leaves 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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without vascular tissue Photosynthetic tissue
Lycophyll Origins Single vascular strand (vein) Stem with vascular tissue Stem, leafy tissue without vascular tissue Stem, leafy tissue with vascular tissue Euphyll Origins Branched vascular strands (veins) Branching stems with vascular tissue Unequal branching Branches in single planes Photosynthetic tissue “webs” branches
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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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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 and attract animals that assist in seed dispersal, expanding the potential range of the species
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Lycophytes Worldwide distribution – abundant in tropics Lack seeds
Ferns and Allies Seed Plants Hornworts Lycophytes Lycophytes Worldwide distribution – abundant in tropics Lack seeds Superficially resemble true mosses Sporophyte dominant 15 PA species
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Princess Pine Dendrolycopodium obscurum
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Shining Club Moss Lycopodium lucidulum
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Ground Pine
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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 Horsetail Ferns Lycophytes Whisk Ferns Seed Plants Ferns Ferns
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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
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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
Antheridium Archegonium Rhizoids Fern life cycle differs from that of a moss Much greater development, independence, and dominance of the fern’s sporophyte Gametophyte lacks vascular tissue Archegonium Egg Sperm Gametophyte MITOSIS Antheridium FERTILIZATION Spores MEIOSIS 1n Zygote 2n n 2n MITOSIS Underside of leaf frond Mature frond Leaf of young sporophyte Adult sporophyte Embryo Mature sporangium Sorus (cluster of sporangia) Gametophyte Sporangium Rhizome
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(left): © Mike Zens/Corbis; (right): © Ed Reschke
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”)
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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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sterile frond fertile frond fiddlehead/crozier rhizome
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Ferns
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Pinnate Pinnatifid
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Not everything that looks like a fern is one!
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…and not everything that is a fern looks like one!
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Matteuccia struthiopteris
Ostrich Fern Matteuccia struthiopteris separate fertile and vegetative fronds
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Sensitive Fern Onoclea sensibilis
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Dennstaedtia punctilobula
Hay-scented Fern Dennstaedtia punctilobula
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