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