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Evolution of Land Plants: Adaptations & Diversity in Plant Kingdom

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  1. CHAPTER 29/30 PLANT DIVERSITY

  2. PLANT EVOLUTION OVERVIEW • STRUCTURAL, CHEMICAL, AND REPRODUCTIVE ADAPTATIONS ENABLED PLANTS TO COLONIZE LAND • PLANTS ARE MULTICELLUAR EUKARYOTES THAT ARE PHOTOSYNTHETIC AUTOTROPHS. PLANTS SHARE THE THE FOLLOWING CHARACTERISTICS WITH THEIR GREEN ALGAL ANCESTORS: • CHLOROPLASTS • CELL WALLS CONTAINING CELLULOSE • FOOD RESERVE THAT IS STARCH STORED IN PLASTIDS

  3. EVOLUTION OF LAND PLANTS • THERE ARE SOME STRUCTURAL FEATURES THAT DISTINGUISH LAND PLANTS FROM ALGAE: • STOMATA: FOR GAS EXCHANGE • WAXY CUTICLE: HELPS CONSERVE WATER • LIGNIN: CELL WALL COMPONENET OF “WOODY” PLANTS • SPOROPOLLENIN: A RESILIENT POLYMER IN THE WALLS OF SPORES AND POLLEN GRAINS

  4. PLANTS AS EMBRYOPHYTES • WITH THE MOVE FROM AN AQUATIC TO TERRESTRIAL ENVIRONMENT, A NEW MODE OF REPRODUCTION WAS NECESSARY TO SOLVE 2 PROBLEMS: • 1) GAMETES MUST BE DISPERSED IN A NONAQUATIC ENVIRONMENT. PLANTS PRODUCE GAMETES WITHIN GAMETANGIA, ORGANS WITH PROTECTIVE JACKETS OF STERILE CELLS THAT PREVENT GAMETES FROM DRYING OUT • 2) EMBRYOS MUST BE PROTECTED AGAINST DESICCATION. THE ZYGOTE DEVELOPS INTO AN EMBRYO THAT IS RETAINED FOR AWHILE WITHIN THE FEMALE GAMETANGIA’S JACKET OF PROTECTIVE CELLS

  5. ALTERNATION OF GENERATIONS • MOST PLANTS REPRODUCE SEXUALLY, AND MOST ARE ALSO CAPABLE OF ASEXUAL PROPAGATION • ALL PLANTS HAVE LIFE CYCLES WITH ALTERNATION OF GENERATIONS • A HAPLOID GAMETOPHYTE GENERATION PRODUCES AND ALTERNATES WITH A DIPOLID SPOROPHYTE GENERATION. THE SPOROPHYTE, IN TURN, PRODUCES GAMETOPHYTES

  6. ALTERNATION OF GENERATIONS

  7. PLANT EVOLUTION • THERE ARE 4 MAJOR PERIODS OF PLANT EVOLUTION THAT OPENED NEW ADAPTIVE ZONES ON LAND • 1) ORIGIN OF PLANTS FROM AQUATIC ANCESTORS ABOUT 475 MYA-VASCULAR TISSUE EVOLVED • 2) DIVERSIFICATION OF SEEDLESS VASCULAR PLANTS, SUCH AS FERNS, ABOUT 400MYA • 3) ORIGIN OF THE SEED NEAR THE END OF THE DEVONIAN, ABOUT 360 MYAS • 4) EMERGENCE OF FLOWERING PLANTS DURING THE EARLY CRETACEOUS, ABOUT 130 MYA

  8. CLASSIFICATION OF PLANTS • NONVASCULAR PLANTS (BRYOPHYTES) • Mosses, liverworts, hornworts • VASCULAR PLANTS (SEEDLESS) • LYCOPHYTES, HORSETAILS, FERNS • VASCULAR PLANTS (SEEDED) • GYNMOSPERMS: conifers, cycads, ginkgo, • ANGIOSPERMS: flowering plants

  9. THE ORIGIN OF PLANTS • PLANTS PROBABLY EVOLVED FROM GREEN ALGAE CALLED CHAROPHYTES • ALTERNATION OF GENERATIONS IN PLANTS MAY HAVE ORIGINATED BY DELAYED MEIOSIS • THIS DELAY MAY MAXIMIZE THE PRODUCTION OF HAPLOID SPORES • IF THE ZYGOTE UNDERGOES MEIOSIS DIRECTLY, EACH FERTILIZATION EVENT RESULTS IN ONLY A FEW HAPLOID SPORES • MITOTIC DIVISION OF THE ZYGOTE TO FORM A MULTICELLULAR SPOROPHYTE AMPLIFIES THE SEXUAL PRODUCT. MANY DIPLOID CELLS CAN UNDERGO MEIOSIS PRODUCING A LARGE NUMBER OF HAPLOID SPORES, ENHANCING THE CHANCES OF SURVIVAL IN UNFAVORABLE ENVIRONMENTS

  10. ADAPTATIONS TO SHALLOW WATER • SOME ADAPTATIONS FOR LIFE IN SHALLOW WATER COULD ALSO HAVE BEEN ADAPTIVE FOR LIFE ON LAND • EXAMPLES: • WAXY CUTICLES • PROTECTION OF GAMETES • PROTECTION OF DEVELOPING EMBRYOS ACCUMULATED ADAPTATIONS MADE IT POSSIBLE FOR ANCESTRAL PLANTS TO LIVE PERMANENTLY ABOVE THE WATER LINE WITH: -SUNLIGHT UNFILTERED BY WATER AND ALGAE -SOIL RICH IN MINERALS -ABSENCE OF TERRESTRIAL HERBIVORES

  11. BRYOPHYTES • THE EMBRYOPHYTE ADAPTATION EVOLVED IN BRYOPHYTES • THE BRYOPHTES INCLUDE PLANTS FOUND IN 3 DIVISIONS: • BRYOPHYTA (MOSSES) • HEPTOPHYTA (LIVERWORTS) • ANTHOCEROPHYTA (HORNWORTS) • SPECIAL ADAPTATIONS HELPED MAKE THE MOVE TO LAND: THE EMBRYOPHTE CONDITION • GAMETANGIA PROTECT DEVELOPING GAMETES • A) ANTHERIDIUM - MALE • B) ARCHEGONIUM- FEMALE

  12. BRYOPHYTES: GAMETOPHYTE IS DOMINANT • BRYOPHYTE LIFE CYCLE ALTERNATES BETWEEN HAPLOID AND DIPLOID • GAMETOPHYTE GENERATIONS IS DOMINANT (WHAT YOU ARE USED TO SEEING AS MOSS PLANTS) • **LOOK AT MOSS LIFE CYCLE ON LASER DISK

  13. MOSSES (BRYOPHYTA) • A TIGHT PACK OF MANY MOSS PLANTS FORMS A SPONGY MAT THAT CAN ABSORB AND RETAIN WATER • EACH PLANT GRIPS THE SUBSTRATUM WITH RHIZOIDS, ELONGATED CELLS OR CELLULAR FILAMENTS • MOSS COVER ABOUT 3% OF THE LAND SURFACE • PHOTOSYNTHESIS OCCURS MOSTLY IN THE SMALL STEMLIKE AND LEAFLIKE STRUCTURE FOUND IN UPPER PARTS OF PLANT

  14. LIVERWORTS(HEPATOPHYTA) • THEY ARE NOT AS ABUNDANT AS MOSS • THEY HAVE A LIFE CYCLE SIMILAR TO MOSSES • THEY CAN ALSO REPRODUCE ASEXUALLY FROM GEMMAE • THEY DISPLAY THEIR GREATEST DIVERSITY IN TROPICAL FORESTS

  15. HORNWORTS (ANTHOCEROPHYTA) • SIMILAR TO LIVERWORTS • THEIR PHOTOSYNTHETIC CELLS HAVE ONLY ONE LARGE CHLOROPLAST, UNLIKE THE MANY SMALLER ONES OF OTHER PLANTS • RECENT MOLECULAR EVIDENCE SUGGEST THAT THEY ARE MOST CLOSELY RELATED TO VASCULAR PLANTS

  16. THE ORIGIN OF VASCULAR PLANTS • IN ADDITION TO CUTICLES AND JACKETED SEX ORGANS, OTHER ADAPTATIONS FOR TERRESTRIAL LIFE EVOLVED IN VASCULAR PLANTS AS THEY COLONIZED LAND: • 1) REGIONAL SPECIALIZATION OF THE PLANT BODY (ROOTS, SHOOTS, LEAVES) • 2) STRUCTURAL SUPPORT(LIGNIN IN CELL WALLS) • 3) VASCULAR SYSYTEM (XYLEM, PHLOEM) • 4) POLLEN(ELIMINATES NEED FOR WATER TO TRANSPORT GAMETES) • 5) SEEDS • 6) INCREASED DOMINANCE OF DIPLOID SPOROPHYTE

  17. SEEDLESS VASCULAR PLANTS • THE EARLIES VASCULAR PLANTS WERE SEEDLESS AND THEY DOMINATED THE CARBONIFEROUS FORESTS. • A SPOROPHYTE-DOMINANT LIFE CYCLE EVOLVED IN SEEDLESS VASCULAR PLANTS • THERE ARE 3 DIVISIONS: • LYCOPHYTES (CLUB MOSSES, GROUND PINE) • SPHENOPHYTA (HORSETAILS) • PTEROPHYTA (FERNS)

  18. FERNS (PTEROPHYTA) • APPEARING IN THE DEVONIAN, FERNS RADIATED INTO DIVERSE SPECIES THAT COEXISTED WITH TREE LYCOPODS AND HORSETAILS IN THE GREAT CARBONIFEROUS FORESTS • FERNS ARE THE MOST WELL REPRESENTED SEEDLESS PLANTS IN MODERN FLORAS. THERE ARE MORE THAN 12,000 EXISTING SPECIES OF FERNS

  19. FERN LIFE CYCLE

  20. SEEDLESS VASCULAR PLANTS MADE COAL • DURING THE CARBONIFEROUIS PERIOD, THE LANDSCAPE WAS DOMINATED BY EXTENSIVE SWAMP FORESTS • ORGANIC RUBBLE OF THE SEEDLESS PLANTS ACCUMULATED AS PEAT • WHEN LATER COVERED BY THE SEA AND SEDIMENTS, HEAT AND PRESSURE TRANSFORMED THE PEAT INTO COAL

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