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Chapter 29

Chapter 29. Plant Diversity I: How Plants Colonized Land. Fig. 29-1. For more than the first 3 billion years of Earth’s history, the terrestrial surface was lifeless. Concept 29.1: Land plants evolved from green algae. Green algae called charophytes are the closest relatives of land plants.

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Chapter 29

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  1. Chapter 29 Plant Diversity I:How Plants Colonized Land

  2. Fig. 29-1 For more than the first 3 billion years of Earth’s history, the terrestrial surface was lifeless

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

  4. Morphological and Molecular Evidence • Many characteristics of land plants also appear in a variety of algal clades, mainly algae • However, land plants share four key traits only with charophytes: • Rose-shaped complexes for cellulose synthesis • Peroxisome enzymes • Structure of flagellated sperm • Formation of a phragmoplast

  5. Comparisons of both nuclear and chloroplast genes point to charophytes as the closest living relatives of land plants • Note that land plants are not descended from modern charophytes, but share a common ancestor with modern charophytes

  6. Fig. 29-3 Chara species, a pond organism 5 mm Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM) 40 µm

  7. Adaptations Enabling the Move to Land • In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out • The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful CO2, nutrient-rich soil, and few herbivores or pathogens • Land presented challenges: a scarcity of water and lack of structural support

  8. The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants • Systematists are currently debating the boundaries of the plant kingdom • Some biologists think the plant kingdom should be expanded to include some or all green algae • Until this debate is resolved, we will retain the embryophyte definition of kingdom Plantae

  9. Fig. 29-4 Red algae ANCESTRAL ALGA Chlorophytes Viridiplantae Charophytes Streptophyta Plantae Embryophytes

  10. Derived Traits of Plants • Four key traits appear in nearly all land plants but are absent in the charophytes: • Alternation of generations (with multicellular, dependent embryos) • Walled spores produced in sporangia • Multicellular gametangia • Apical meristems

  11. Additional derived traits such as a cuticle and secondary compounds evolved in many plant species • Symbiotic associations between fungi and the first land plants may have helped plants without true roots to obtain nutrients

  12. Fig. 29-5a Gamete from another plant Gametophyte (n) Mitosis Mitosis n n n n Spore Gamete MEIOSIS FERTILIZATION Zygote 2n Mitosis Sporophyte (2n) Alternation of generations

  13. Fig. 29-5b Embryo 2 µm Maternal tissue Wall ingrowths 10 µm Placental transfer cell (outlined in blue) Embryo (LM) and placental transfer cell (TEM) of Marchantia (a liverwort)

  14. Fig. 29-5c Spores Sporangium Longitudinal section of Sphagnum sporangium (LM) Sporophyte Gametophyte Sporophytes and sporangia of Sphagnum (a moss)

  15. Fig. 29-5d Archegonium with egg Female gametophyte Antheridium with sperm Male gametophyte Archegonia and antheridia of Marchantia (a liverwort)

  16. Fig. 29-5e Apical meristems Developing leaves Apical meristem of shoot Apical meristem of root Shoot Root 100 µm 100 µm

  17. Fig. 29-6 (a) Fossilized spores Fossil evidence indicates that plants were on land at least 475 million years ago (b) Fossilized sporophyte tissue

  18. Table 29-1 Club mosses ferns

  19. Fig. 29-7 Origin of land plants (about 475 mya) 1 Origin of vascular plants (about 420 mya) 2 Origin of extant seed plants (about 305 mya) 3 Liverworts Nonvascular plants (bryophytes) Land plants Hornworts ANCES- TRAL GREEN ALGA 1 Mosses Lycophytes (club mosses, spike mosses, quillworts) Seedless vascular plants Vascular plants 2 Pterophytes (ferns, horsetails, whisk ferns) Gymnosperms 3 Seed plants Angiosperms 50 500 450 400 0 350 300 Millions of years ago (mya)

  20. Bryophyte Gametophytes • In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes • Sporophytes are typically present only part of the time

  21. Fig. 29-8-3 Raindrop Sperm “Bud” Antheridia Male gametophyte (n) Key Haploid (n) Protonemata (n) Diploid (2n) “Bud” Egg Gametophore Spores Archegonia Female gametophyte (n) Spore dispersal Rhizoid Peristome FERTILIZATION Sporangium (within archegonium) MEIOSIS Seta Zygote (2n) Capsule (sporangium) Mature sporophytes Foot Embryo Archegonium Young sporophyte (2n) 2 mm Female gametophytes Capsule with peristome (SEM)

  22. Fig. 29-9d Polytrichum commune, hairy-cap moss Sporophyte (a sturdy plant that takes months to grow) Capsule Seta Gametophyte

  23. Fig. 29-11 (a) Peat being harvested (b) “Tollund Man,” a bog mummy

  24. Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall • Bryophytes and bryophyte-like plants were the prevalent vegetation during the first 100 million years of plant evolution • Vascular plants began to diversify during the Devonian and Carboniferous periods • Vascular tissue allowed these plants to grow tall • Seedless vascular plants have flagellated sperm and are usually restricted to moist environments

  25. Origins and Traits of Vascular Plants • Fossils of the forerunners of vascular plants date back about 420 million years • These early tiny plants had independent, branching sporophytes • Living vascular plants are characterized by: • Life cycles with dominant sporophytes • Vascular tissues called xylem and phloem • Well-developed roots and leaves

  26. Fig. 29-13-3 Key Haploid (n) Diploid (2n) Antheridium Spore (n) Young gametophyte Spore dispersal MEIOSIS Sporangium Mature gametophyte (n) Sperm Archegonium Egg Mature sporophyte (2n) New sporophyte Sporangium Zygote (2n) FERTILIZATION Sorus Gametophyte Fiddlehead

  27. Transport in Xylem and Phloem • Vascular plants have two types of vascular tissue: xylem and phloem • Xylem conducts most of the water and minerals and includes dead cells called tracheids • Phloem consists of living cells and distributes sugars, amino acids, and other organic products • Water-conducting cells are strengthened by lignin and provide structural support • Increased height was an evolutionary advantage

  28. Evolution of Roots • Roots are organs that anchor vascular plants • They enable vascular plants to absorb water and nutrients from the soil • Roots may have evolved from subterranean stems

  29. Evolution of Leaves • Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis

  30. Fig. 29-16

  31. Fig. 29-UN4 Apical meristem of shoot Developing leaves Gametophyte Mitosis Mitosis n n n n Gamete Spore MEIOSIS FERTILIZATION Zygote 2n Mitosis Haploid Sporophyte Diploid Alternation of generations 1 Apical meristems 2 Sporangium Spores Archegonium with egg Antheridium with sperm Multicellular gametangia Walled spores in sporangia 3 4

  32. Chapter 30 Plant Diversity II: The Evolution of Seed Plants

  33. Fig. 30-1 A seed consists of an embryo and nutrients surrounded by a protective coat

  34. Concept 30.1: Seeds and pollen grains are key adaptations for life on land • In addition to seeds, the following are common to all seed plants • Reduced gametophytes • Heterospory • Ovules • Pollen

  35. Fig. 30-2 PLANT GROUP Mosses and othernonvascular plants Ferns and other seedlessvascular plants Seed plants (gymnosperms and angiosperms) Reduced, independent(photosynthetic andfree-living) Reduced (usually microscopic), dependent on surroundingsporophyte tissue for nutrition Gametophyte Dominant Reduced, dependent ongametophyte for nutrition Sporophyte Dominant Dominant Gymnosperm Angiosperm Sporophyte(2n) Microscopic femalegametophytes (n) insideovulate cone Microscopic femalegametophytes (n) insidethese partsof flowers Sporophyte(2n) Gametophyte(n) Example Microscopic malegametophytes (n) insidethese partsof flowers Microscopic malegametophytes (n) inside pollencone Sporophyte (2n) Sporophyte (2n) Gametophyte(n)

  36. Fig. 30-3-4 Seed coat(derived fromintegument) Integument Femalegametophyte (n) Spore wall Egg nucleus (n) Immaturefemale cone Food supply(femalegametophytetissue) (n) Male gametophyte(within a germinatedpollen grain) (n) Megasporangium(2n) Dischargedsperm nucleus (n) Embryo (2n)(new sporophyte) Micropyle Pollen grain (n) Megaspore (n) (a) Unfertilized ovule (b) Fertilized ovule (c) Gymnosperm seed

  37. Concept 30.2: Gymnosperms bear “naked” seeds, typically on cones • The gymnosperms have “naked” seeds not enclosed by ovaries and consist of four phyla: • Cycadophyta (cycads) • Gingkophyta (one living species: Ginkgo biloba) • Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) • Coniferophyta (conifers, such as pine, fir, and redwood)

  38. Living seed plants can be divided into two clades: gymnosperms and angiosperms • Gymnosperms appear early in the fossil record and dominated the Mesozoic terrestrial ecosystems • Gymnosperms were better suited than nonvascular plants to drier conditions • Today, cone-bearing gymnosperms called conifers dominate in the northern latitudes

  39. Phylum Cycadophyta • Individuals have large cones and palmlike leaves • These thrived during the Mesozoic, but relatively few species exist today

  40. Fig. 30-5a Cycas revoluta

  41. Phylum Ginkgophyta • This phylum consists of a single living species, Ginkgo biloba • It has a high tolerance to air pollution and is a popular ornamental tree

  42. Fig. 30-5b Ginkgo bilobapollen-producing tree

  43. Fig. 30-5c Ginkgo bilobaleaves and fleshy seeds

  44. Phylum Gnetophyta • This phylum comprises three genera • Species vary in appearance, and some are tropical whereas others live in deserts

  45. Fig. 30-5d Gnetum

  46. Fig. 30-5e Ephedra

  47. Fig. 30-5f Welwitschia

  48. Fig. 30-5g Ovulate cones Welwitschia

  49. Phylum Coniferophyta • This phylum is by far the largest of the gymnosperm phyla • Most conifers are evergreens and can carry out photosynthesis year round

  50. Fig. 30-5h Douglas fir

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