1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 29 Plant Diversity I How Plants Colonized Land

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An Overview of Land Plant Evolution For more than the first 3 billion years of Earth’s history the terrestrial surface was lifeless Since colonizing land plants have diversified into roughly 290,000 living species Land plants evolved from green algae (chlorophyta): – Researchers have identified green algae called charophyceans as the closest relatives of land plants

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of Plants The first plants evolved from an organism much like the multicellular green algae living today – However, the evolution of plants favored species that were more resistant to the drying rays of the sun!

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview of Land Plant Evolution > 280,000 species of plants inhibit Earth today. 4 major evolutionary trends characterize plants today: – Movement to land (new niches) – Development of vascular tissue (taller growth) – Development of seeds (dispersal of offspring) – Development of flowers (pollinators)

5. Figure 29.1 Some highlights of plant evolution

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Morphological and Biochemical Evidence Land plants evolved from charophycean algae over 500 million years ago. There are four key traits that land plants share only with charophyceans: – Rose-shaped complexes for cellulose synthesis Rose-shaped array of proteins that synthesize the cellulose microfibrils of the cell wall – Peroxisome enzymes Help minimize the loss of organic product due to photorespiration – Structure of flagellated sperm Used for sperm motility – Formation of a phragmoplast An alignment of cytoskeletal elements and Golgi-derived vesicles across the midline of the dividing cell.

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Derived Traits of Plants Five key traits appear in nearly all land plants but are absent in the charophyceans: – Apical meristems – Multicellular dependent embryos – Alternation of generations – Walled spores produced in sporangia – Multicellular gametangia

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Apical Meristems – Producers of Plant’s Tissues These are localized regions of cell division at the tips of shoots and roots. – Maximize their exposure to environmental resources. Apical meristem of shoot Developing leaves Apical meristem of root

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Multicellular Dependent Embryos Multicellular plant embryos develop from zygotes that are retained within tissues of the female parent. – Parental tissues provide developing embryo with nutrients.

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Alternation of Generations Life Cycle During the life cycle of ALL land plants, two multicellular body forms alternate, each form producing the other. – Called alternation of generations – Cells of gametophyte generation are haploid (single set of chromosomes) – produces gametes Fusion of gametes (eggs and sperm) during fertilization forms diploid zygotes. – Mitotic division of the zygote produces the multicellular sporophyte (diploid). Meiosis in a mature sporophyte produces haploid reproductive cells called spores (reproductive cells that can develop into a new organism without fusing with another cell). Mitotic division of spore produces new gametophyte…so cycle continues.

11. Figure 29.6 Alternation of generations: a generalized scheme

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Walled Spores Produced in Sporangia Plant spores are haploid reproductive cells that have the potential to grow into multicellular, haploid gametophytes by mitosis. – A polymer called sporopollenin (durable organic material) makes walls of plant spores tough and resistant to harsh environments. – Multicellular organs called sporangia, found on the sporophyte generation of a plant, produce the spores. – The outer tissues of the sporangium protect developing spores until they are ready to be released – a key adaptation in land plants.

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Multicellular Gametangia The gametophyte forms of bryophytes, pteridophytes, and gymnosperms all produce their gametes within multicellular organs called gametangia. – Female gametangia are called archegonia – Male gametangia are called antheridia

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other Terrestrial Adaptations Common to Land Plants Adaptations for water conservation – Cuticle (waxy cover on surface of stems and leaves) – Stomata (pore on leaves allowing for gas exchange) Adaptations for Water Transport – Xylem (carries water and minerals from roots to rest of plant) – Phloem (carries sugars and other nutrients throughout plant)

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4 Main Groups of Land Plants Bryophytes: non-vascular plants – mosses, hornworts, and liverworts Pteridophytes: seedless vascular plants – Club moss, horsetails, ferns Gymnosperms: vascular seeded cone-bearers – Ginkgos, cycads, gnetophytes, conifers Angiosperms: vascular seeded flowering plants – Monocots & dicots

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cone-bearing plants 760 species Ferns and their relatives 11,000 species Mosses and their relatives 15,600 species Flowering plants 235,000 species Section 22-1 Figure 22-7 The Diversity of Plants Go to Section: Land plants can be informally grouped based on the presence or absence of vascular tissue

17. Table 29.1 Ten Phyla of Extant Plants

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An Overview of Land Plant Evolution Bryophytes (nonvascular plants) Seedless vascular plants Seed plants Vascular plants Land plants Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga Charophyceans Liverworts Hornworts Mosses Lycophytes (club mosses, spike mosses, quillworts) Pterophyte (ferns, horsetails, whisk fern) Gymnosperms Angiosperms Figure 29.7

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bryophytes – Nonvascular Plants 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 In all three bryophyte phyla – Gametophytes are larger and longer-living than sporophytes – Water is required for survival AND reproduction – absorb water by diffusion – Have no true roots, stems, and leaves and lack lignin-fortified tissue required to support tall plants on land

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life Cycle of Moss

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bryophyte Diversity LIVERWORTS (PHYLUM HEPATOPHYTA) HORNWORTS (PHYLUM ANTHOCEROPHYTA) MOSSES (PHYLUM BRYOPHYTA) Gametophore of female gametophyte Marchantia polymorpha, a “thalloid” liverwort Foot Sporangium Seta 500 µm Marchantia sporophyte (LM) Plagiochila deltoidea, a “leafy” liverwort An Anthoceros hornwort species Sporophyte Gametophyte Polytrichum commune, hairy-cap moss Sporophyte Gametophyte Figure 29.9

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tracheophytes – Vascular Plants Most common and widespread of land plants Have true vascular tissues -- xylem and phloem that allow true “organs” to develop – roots, stems, leaves – Xylem carries water and minerals in a plant – Phloem carries nutrients in a plant Two categories – Seedless (reproduce by spores) – Seeded (reproduce by seeds)

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life Cycles with Dominant Sporophytes In contrast with bryophytes – The sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern – The gametophytes are tiny plants that grow on or below the soil surface

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Life Cycle of a Fern Fern sperm use flagella to swim from the antheridia to eggs in the archegonia. 4 Sporangia release spores. Most fern species produce a single type of spore that gives rise to a bisexual gametophyte. 1 The fern spore develops into a small, photosynthetic gametophyte. 2 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanisms promote cross-fertilization between gametophytes. 3 On the underside of the sporophyte‘s reproductive leaves are spots called sori. Each sorus is a cluster of sporangia. 6 A zygote develops into a new sporophyte, and the young plant grows out from an archegonium of its parent, the gametophyte. 5 MEIOSIS Sporangium Mature sporophyte New sporophyte Zygote FERTILIZATION Archegonium Egg Haploid (n) Diploid (2n) Spore Young gametophyte Fiddlehead Antheridium Sperm Gametophyte Key Sorus Figure 29.12

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Transport in Xylem and Phloem Vascular plants have two types of vascular tissue: xylem and phloem Xylem – Conducts most of the water and minerals – Includes dead cells called tracheids Phloem – Distributes sugars, amino acids, and other organic products – Consists of living cells

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of Roots Roots are organs that anchor vascular plants – Enable vascular plants to absorb water and nutrients from the soil – May have evolved from subterranean stems

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of Leaves Leaves – Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis Leaves are categorized by two types – Microphylls, leaves with a single vein – Megaphylls, leaves with a highly branched vascular system

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sporophylls and Spore Variations Sporophylls are modified leaves with sporangia Most seedless vascular plants are homosporous, producing one type of spore that develops into a bisexual gametophyte All seed plants and some seedless vascular plants are heterosporous, having two types of spores that give rise to male and female gametophytes

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Life Cycle of a Fern Fern sperm use flagella to swim from the antheridia to eggs in the archegonia. 4 Sporangia release spores. Most fern species produce a single type of spore that gives rise to a bisexual gametophyte. 1 The fern spore develops into a small, photosynthetic gametophyte. 2 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanisms promote cross-fertilization between gametophytes. 3 On the underside of the sporophyte‘s reproductive leaves are spots called sori. Each sorus is a cluster of sporangia. 6 A zygote develops into a new sporophyte, and the young plant grows out from an archegonium of its parent, the gametophyte. 5 MEIOSIS Sporangium Mature sporophyte New sporophyte Zygote FERTILIZATION Archegonium Egg Haploid (n) Diploid (2n) Spore Young gametophyte Fiddlehead Antheridium Sperm Gametophyte Key Sorus Figure 29.12

30. Figure 29.24b Fern sporophyll, a leaf specialized for spore production

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Classification of Seedless Vascular Plants Seedless vascular plants form two phyla – Lycophyta, including club mosses, spike mosses, and quillworts – Pterophyta, including ferns, horsetails, and whisk ferns and their relatives Since they don’t have seeds, they need LOTS of water for fertilization – USE SPORES TO REPRODUCE FOR MAJORITY OF LIFE; gametes are used only for a short period of time Display alternation of generations – part of time is asexual (uses spores), part is sexual (uses gametes)

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings General Groups of Seedless Vascular Plants LYCOPHYTES (PHYLUM LYCOPHYTA) PTEROPHYTES (PHYLUM PTEROPHYTA) WHISK FERNS AND RELATIVES HORSETAILS FERNS Isoetes gunnii, a quillwort Selaginella apoda, a spike moss Diphasiastrum tristachyum, a club moss Strobili (clusters of sporophylls) Psilotum nudum, a whisk fern Equisetum arvense, field horsetail Vegetative stem Strobilus on fertile stem Athyrium filix-femina, lady fern Figure 29.14

33. Figure 29.21 Pteridophytes: club "moss" (top left), whisk fern (top right), horsetail (bottom left), fern (bottom right)

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts Modern species of lycophytes – Are relics from a far more eminent past – Are small herbaceous plants

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives Ferns – Are the most diverse seedless vascular plants

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Significance of Seedless Vascular Plants The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Carboniferous, forming the first forests Figure 29.15

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Significance of Seedless Vascular Plants The growth of these early forests – May have helped produce the major global cooling that characterized the end of the Carboniferous period – Decayed and eventually became coal

38. Evolution of Plants Flowering plants Cone-bearing plants Ferns and their relatives Mosses and their relatives Green algae ancestor Flowers; Seeds Enclosed in Fruit Seeds Water-Conducting (Vascular) Tissue Vascular w/ Seeds Angiosperms Vascular w/ Seeds Gymnosperms Vascular Seedless Pterophyta Non-Vascular Bryophytes