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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. 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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. 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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 23 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