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Chapter 29

Chapter 29. Plant Diversity I How Plants Colonized Land. Concept 29.1: Land plants evolved from green algae. Green algae called charophyceans are the closest relatives of land plants. Morphological and Biochemical Evidence.

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Chapter 29

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  1. Chapter 29 Plant Diversity IHow Plants Colonized Land

  2. Concept 29.1: Land plants evolved from green algae • Green algae called charophyceans are the closest relatives of land plants

  3. Morphological and Biochemical Evidence • However, land plants share four key traits only with charophyceans: • Similar chloroplasts • Peroxisome enzymes • Structure of flagellated sperm • Walls with cellulose

  4. LE 29-3 Chara, a pond organism (LM). 10 mm 40 µm Coleochaete orbicularis, a disk-shaped charophycean (LM).

  5. Concept 29.2: Land plants possess a set of derived terrestrial adaptations Viridiplantae Streptophyta Plantae • Many adaptations emerged after land plants diverged from their charophycean relatives Charophyceans Red algae Embryophytes Chlorophytes Ancestral alga

  6. Derived Traits of Plants • Five key traits appear in nearly all land plants but are absent in the charophyceans: • Apical meristems • Alternation of generations • Walled spores produced in sporangia • Multicellular gametangia • Multicellular dependent embryos

  7. LE 29-5a Apical Meristems Apical Meristem of shoot Developing leaves Apical meristem Shoot Root 100 µm 100 µm

  8. LE 29-5b Alternation of Generations Haploid multicellular organism (gametophyte) Mitosis Mitosis Gametes Spores MEIOSIS FERTILIZATION Zygote Mitosis Diploid multicellular organism (sporophyte)

  9. LE 29-5c Walled Spores Produced in Sporangia Multicellular Gametangia Multicellular, Dependent Embryos Archegonium with egg Longitudinal section of Sphagnum sporangium (LM) Female gametophyte Spores Embryo Maternal tissue Sporangium 10 µm 2 µm Sporophyte Antheridium with sperm Male gametophyte Gametophyte Wall ingrowths Placental transfer cell Archegonia and antheridia of Marchantia (a liverwort) Sporophyte and sporangium of Sphagnum (a moss)

  10. Additional derived traits such as a cuticle evolved in many plant species

  11. Fossilized spores. Unlike the spores of most living plants, which are single grains, these spores found in Oman are in groups of four (left; one hidden) and two (right). The Origin and Diversification of Plants • Fossil evidence indicates that plants were on land at least 475 million years ago Fossilized sporophyte tissue. The spores were embedded in tissue that appears to be from plants.

  12. LE 29-7 Land plants Vascular plants Bryophytes Seedless vascular plants Seed plants Gymno- sperms Angio- sperms Hornworts Mosses Liverworts Lycophytes Pterophytes Charophyceans Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga

  13. Concept 29.3: The life cycles of mosses and other bryophytes are dominated by the gametophyte stage • Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants: • Liverworts, phylum Hepatophyta • Hornworts, phylum Anthocerophyta • Mosses, phylum Bryophyta

  14. Bryophyte Gametophytes • In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes • Sporophytes are typically present only part of the time Animation: Moss Life Cycle

  15. LE 29-8 Raindrop Key Male gametophyte Haploid (n) Diploid (2n) Sperm “Bud” Spores develop into threadlike protonemata. A sperm swims through a film of moisture to an archegonium and fertilizes the egg. Antheridia The haploid protonemata produce “buds” that grow into gametophytes. Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively. Protonemata “Bud” Egg Gametophore Spores Female gametophyte Archegonia Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores. Rhizoid Peristome The sporophyte grows a long stalk, or seta, that emerges from the archegonium. FERTILIZATION Sporangium (within archegonium) MEIOSIS Seta Calyptra Zygote Capsule (sporangium) Mature sporophytes Foot Embryo Archegonium The diploid zygote develops into a sporophyte embryo within the archegonium. Young sporophyte Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte. Female gametophytes Capsule with peristome (SEM)

  16. Bryophyte gametophytes • Produce flagellated sperm in antheridia • Produce ova in archegonia • Generally form ground-hugging carpets and are at most only a few cells thick

  17. Bryophyte Sporophytes • Bryophyte sporophytes • Grow out of archegonia • Are the smallest and simplest of all extant plant groups • Consist of a foot, a seta, and a sporangium

  18. LE 29-9a Gametophore of female gametophyte 500 µm Foot Seta Sporangium Marchantia polymorpha, a “thalloid” liverwort Marchantia sporophyte (LM)

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