1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 29 Plant Diversity I: How Plants Colonized Land

2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: The Greening of Earth 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 Plants supply oxygen and are the ultimate source of most food eaten by land animals

3. Fig. 29-1

4. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 29.1: Land plants evolved from green algae Land plants evolved from green algae Researchers have identified green algae called charophytes as: – The closest relatives of land plants

5. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Morphological and Molecular Evidence Many characteristics of land plants also appear in a variety of protists, mainly algae Protists include: Plants, animals, fungi, & algae However, land plants share four key traits only with charophytes (green algae) : – Rose-shaped complexes for cellulose synthesis – Peroxisome enzymes – Structure of flagellated sperm – Formation of a phragmoplast

6. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Morphological and Molecular Evidence Phragmoplast: Microtubules connecting the two daughter nuclei of a dividing cell A cell plate develops in the middle of the phragmoplast across the midline of the dividing cell A cell plate then gives rise to new cross wall (new cell wall) that separates the daughter cells

7. Fig. 29-2 30 nm

8. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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/living charophytes, but Share a common ancestor with modern charophytes

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

10. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Adaptations Enabling the Move to Land Sporopollenin: – A durable polymer layer in charophytes protecting exposed zygotes from drying out The movement onto land provided: – Unfiltered sun – More plentiful CO 2 – Nutrient-rich soil – Few herbivores or pathogens Land also presented challenges: – Scarcity of water – Lack of structural support (e.g gravity)

11. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Accumulation of traits facilitating survival on land has triggered land colonization by plants Systematists currently debating the boundaries of the plant kingdom Some think the plant kingdom should be expanded to include some or all the green algae Until this debate is resolved, embryophyte ( plants with embryos) will be retained as the definition of the kingdom Plantae

12. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Derived Traits of Plants Four key traits appear in nearly all land plants but are absent in the charophytes: – Alternation of generations – Walled spores produced in sporangia – Multicellular gametangia – Apical meristems

13. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Additional derived traits evolved in many plant species such as: – A cuticle (epidermal waxy covering) – Secondary compounds (bitter protective comp) Symbiotic associations: – Between fungi and the first land plants – May have helped plants without true roots to obtain nutrients

14. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Alternation of Generations Plants alternate between two multicellular stages, This is a reproductive cycle called alternation of generations: – The gametophyte is haploid and produces haploid gametes by mitosis – The sporophyte is diploid, resulting from the fusion of the gametes, and produces haploid spores by meiosis

15. Fig. 29-5a Gametophyte (n) Gamete from another plant n n Mitosis Gamete FERTILIZATIONMEIOSIS Mitosis Spore n n 2n2n Zygote Mitosis Sporophyte (2n) Alternation of generations

16. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The diploid embryo is retained within the tissue of the female gametophyte Nutrients are transferred from parent to embryo through placental transfer cells Land plants are called embryophytes because of the dependency of the embryo on the parent Multicellular, Dependent Embryos

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

18. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Walled Spores Produced in Sporangia The sporophyte produces spores in organs called sporangia Diploid cells called sporocytes undergo meiosis to generate haploid spores Spore walls contain sporopollenin, which makes them resistant to harsh environments

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

20. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Multicellular Gametangia Gametes are produced within organs called gametangia Female gametangia, called archegonia, produce eggs and are the site of fertilization Male gametangia, called antheridia, are the site of sperm production and release

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

22. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Apical Meristems Plants sustain continual growth in their apical meristems Cells from the apical meristems differentiate into various tissues

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

24. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Origin and Diversification of Plants Fossil evidence indicates that plants were on land at least 475 million years ago Fossilized spores and tissues have been extracted from 475-million-year-old rocks

25. Fig. 29-6 (a) Fossilized spores (b) Fossilized sporophyte tissue

26. Whatever the age of the first land plants: –Those ancestral species gave rise to a vast diversity of modern plants

27. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Based on the presence or absence of vascular tissue, land plants are informally grouped into: – Nonvascular plants: Are commonly called bryophytes – Vascular plants: Most plants have vascular tissue

28. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Seedless vascular plants can be divided into: – Lycophytes (club mosses and their relatives) – Pterophytes (ferns and their relatives) Seedless vascular plants are: – Paraphyletic (not monophyletic=not a clade=don’t share a common ancestor), – Are of the same level of biological organization, & called grade (instead of a clade) Seedless Vascular Plants

29. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings A seed is an embryo & nutrients surrounded by a protective coat Seed plants (a clade of vascular plants) : Are the vast majority of living plant species Divided into further clades based on where seeds mature, : – Gymnosperms: seed maturation is not in enclosed chambers; ex. conifers – Angiosperms: seeds mature in enclosed chambers called ovaries; ex. all flowering plants Vascular Plants with seeds

30. Fig. 29-7 Origin of land plants (about 475 mya) 1 2 3 1 2 3 Origin of vascular plants (about 420 mya) Origin of extant seed plants (about 305 mya) ANCES- TRAL GREEN ALGA Liverworts Hornworts Mosses Lycophytes (club mosses, spike mosses, quillworts) Pterophytes (ferns, horsetails, whisk ferns) Gymnosperms Angiosperms Seed plants Seedless vascular plants Nonvascular plants (bryophytes) Land plants Vascular plants Millions of years ago (mya) 500450400 350300 50 0

31. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mosses and other nonvascular plants have life cycles dominated by gametophytes Bryophytes (non-vascular plants): Represented today by three phyla of small herbaceous (nonwoody) plants: – Liverworts, phylum Hepatophyta – Hornworts, phylum Anthocerophyta – Mosses, phylum Bryophyta Mosses are most closely related to vascular plants

32. Fig. 29-UN1 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms

33. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyte Gametophytes Compared to sporophytes in all three bryophyte phyla, gametophytes are: Larger Live longer Sporophytes are typically present only part of the time

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

35. Fig. 29-8a Capsule with peristome (SEM) 2 mm

36. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings A spore germinates into a gametophyte, which is composed of: – A protonema (green, branched one-cell filaments) – Gametophore(s) (gamete-producing structure (s)) Rhizoids (tubular/filament one-cell structures): – anchor gametophytes to substrate

37. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The height of gametophytes is constrained by lack of vascular tissues Mature gametophytes produce: – Flagellated sperm in antheridia, and – An egg in each archegonium Sperm swim through a film of water to reach and fertilize the egg

38. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyte Sporophytes Bryophyte sporophytes: – Green & photosynthetic when young, but can’t live independantly – Remain attached to parent gametophyte – The smallest & simplest sporophytes of all extant plant groups

39. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyte Sporophytes A sporophyte consists of a: – Foot: (embeded in archegonium; absorbs nutrient from gametophyte) – Seta: (stalk; conduct nutrients to sporangium) – Sporangium, also called a capsule: (produces spores & discharges them through a peristome – Peristome: (a ring of interlocking tooth-like structures for spore discharge) Some sporophytes have stomata (pores for gas”O2&Co2” exchange & water evaporation)

40. Fig. 29-9a Thallus Gametophore of female gametophyte Marchantia polymorpha, a “thalloid” liverwort Marchantia sporophyte (LM) Sporophyte Foot Seta Capsule (sporangium) 500 µm

41. Fig. 29-9b Plagiochila deltoidea, a “leafy” liverwort

42. Fig. 29-9c An Anthoceros hornwort species Sporophyte Gametophyte

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

44. Fig. 29-11a (a) Peat being harvested

45. Fig. 29-11b (b) “Tollund Man,” a bog mummy

46. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Seedless Vascular Plants (Ferns and other) were the first plants to grow tall Bryophytes and bryophyte-like plants: – 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 them to grow tall Seedless vascular plants have: – Flagellated sperm – Usually restricted to moist environments

47. Fig. 29-UN2 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms

48. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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

49. Fig. 29-12 Sporophytes of Aglaophyton major

50. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Life Cycles with Dominant Sporophytes In contrast with bryophytes: – 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 Animation: Fern Life Cycle Animation: Fern Life Cycle

51. Fig. 29-13-3 Key Haploid (n) Diploid (2n) MEIOSIS Spore dispersal Sporangium Mature sporophyte (2n) Sorus Fiddlehead Spore (n) Young gametophyte Mature gametophyte (n) Archegonium Egg Antheridium Sperm FERTILIZATION New sporophyte Gametophyte Zygote (2n) The life cycle of a fern

52. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Transport in Xylem and Phloem Vascular plants have two types of vascular tissue: – Xylem: includes dead cells called tracheids conducts most of the water and minerals – Phloem: consists of living cells 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

53. Copyright © 2008 Pearson Education, Inc., publishing as Pearson 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

54. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution of Leaves Leaves: – Are organs that increase the surface area of vascular plants, – Thereby, able to capture more solar energy that is used for photosynthesis

55. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Leaves are categorized by two types: – Microphylls – Leaves with a single vein – Megaphylls: – Leaves with a highly branched vascular system According to one model of evolution: Microphylls evolved first, as outgrowths of stems

56. Fig. 29-14 Vascular tissue SporangiaMicrophyll (a) Microphylls (b) Megaphylls Overtopping growth Megaphyll Other stems become re- duced and flattened. Webbing develops.

57. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Sporophylls and Spore Variations Sporophylls: – Are modified leaves with sporangia

58. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Most seedless vascular plants are homosporous, producing: – One type of spore that develops into a bisexual gametophyte All seed plants & some seedless vascular plants are heterosporous, produceing: – megaspores that give rise to female gametophytes, and – microspores that give rise to male gametophytes

59. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Classification of Seedless Vascular Plants There are two phyla of seedless vascular plants: – Phylum Lycophyta includes: – club mosses, spike mosses, and quillworts – Phylum Pterophyta includes: – ferns, horsetails, and whisk ferns and their relatives

60. Fig. 29-15a Lycophytes (Phylum Lycophyta) Selaginella apoda, a spike moss Isoetes gunnii, a quillwort Strobili (clusters of sporophylls) 2.5 cm Diphasiastrum tristachyum, a club moss 1 cm

61. Fig. 29-15e Pterophytes (Phylum Pterophyta) Athyrium filix-femina, lady fern Vegetative stem Strobilus on fertile stem 1.5 cm 25 cm 2.5 cm Psilotum nudum, a whisk fern Equisetum arvense, field horsetail