1. Mr. Karns AP biology for Biology, Seventh Edition Neil Campbell and Jane Reece Chapter 29 Plant Diversity I How Plants Colonized Land

2. Overview: The Greening of Earth Looking at a lush landscape – It is difficult to imagine the land without any plants or other organisms Figure 29.1

3. 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

4. Concept 29.1: Land plants evolved from green algae Researchers have identified green algae called charophyceans as the closest relatives of land plants

5. Morphological and Biochemical Evidence Many characteristics of land plants – Also appear in a variety of algal clades

6. There are four key traits that land plants share only with charophyceans – Rose-shaped complexes for cellulose synthesis 30 nm Figure 29.2

7. – Peroxisome enzymes – Structure of flagellated sperm – Formation of a phragmoplast

8. Genetic Evidence Comparisons of both nuclear and chloroplast genes – Point to charophyceans as the closest living relatives of land plants Chara, a pond organism (a) 10 mm Coleochaete orbicularis, a disk- shaped charophycean (LM) (b) 40 µm Figure 29.3a, b

9. Adaptations Enabling the Move to Land In charophyceans – A layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out The accumulation of traits that facilitated survival on land – May have opened the way to its colonization by plants

10. Concept 29.2: Land plants possess a set of derived terrestrial adaptations Many adaptations – Emerged after land plants diverged from their charophycean relatives

11. Defining the Plant Kingdom Systematists – Are currently debating the boundaries of the plant kingdom Plantae Streptophyta Viridiplantae Red algaeChlorophytesCharophyceansEmbryophytes Ancestral alga Figure 29.4

12. Some biologists think that the plant kingdom – Should be expanded to include some or all green algae Until this debate is resolved – This textbook retains the embryophyte definition of kingdom Plantae

13. 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

14. APICAL MERISTEMS Apical meristem of shoot Developing leaves 100 µm Apical meristems of plant shoots and roots. The light micrographs are longitudinal sections at the tips of a shoot and root. Apical meristem of root Root 100 µm Shoot Figure 29.5 Apical meristems and alternation of generations Haploid multicellular organism (gametophyte) Mitosis Gametes Zygote Diploid multicellular organism (sporophyte) Alternation of generations: a generalized scheme MEIOSISFERTILIZATION 2n2n 2n2n n n n n n Spores Mitosis ALTERNATION OF GENERATIONS Figure 29.5

15. Walled spores; multicellular gametangia; and multicellular, dependent embryos WALLED SPORES PRODUCED IN SPORANGIA MULTICELLULAR GAMETANGIA MULTICELLULAR, DEPENDENT EMBRYOS Spores Sporangium Longitudinal section of Sphagnum sporangium (LM) Sporophyte Gametophyte Sporophyte and sporangium of Sphagnum (a moss) Female gametophyte Archegonium with egg Antheridium with sperm Male gametophyte Archegonia and antheridia of Marchantia (a liverwort) Embryo Maternal tissue 2 µm Wall ingrowths Placental transfer cell 10 µm Embryo and placental transfer cell of Marchantia Figure 29.5

16. Additional derived units – Such as a cuticle and secondary compounds, evolved in many plant species

17. The Origin and Diversification of Plants Fossil evidence – Indicates that plants were on land at least 475 million years ago

18. Fossilized spores and tissues – Have been extracted from 475-million-year-old rocks 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). (a) Fossilized sporophyte tissue. The spores were embedded in tissue that appears to be from plants. (b) Figure 29.6 a, b

19. Whatever the age of the first land plants – Those ancestral species gave rise to a vast diversity of modern plants Table 29.1

20. Land plants can be informally grouped – Based on the presence or absence of vascular tissue

21. 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

22. 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

23. Debate continues over the sequence of bryophyte evolution Mosses are most closely related to vascular plants

24. Bryophyte Gametophytes In all three bryophyte phyla – Gametophytes are larger and longer-living than sporophytes – It is the dominant generation – Also photosynthetic

25. The life cycle of a moss Mature sporophytes Young sporophyte Male gametophyte Raindrop Sperm Key Haploid (n) Diploid (2n) Antheridia Female gametophyte Egg Archegonia FERTILIZATION (within archegonium) Zygote Archegonium Embryo Female gametophytes Gametophore Foot Capsule (sporangium) Seta Peristome Spores Protonemata “Bud” MEIOSIS Sporangium Calyptra Capsule with peristome (LM) Rhizoid Mature sporophytes Spores develop into threadlike protonemata. 1 The haploid protonemata produce “buds” that grow into gametophytes. 2 Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively. 3 A sperm swims through a film of moisture to an archegonium and fertilizes the egg. 4 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. 8 The sporophyte grows a long stalk, or seta, that emerges from the archegonium. 6 The diploid zygote develops into a sporophyte embryo within the archegonium. 5 Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte. 7 Figure 29.8

26. 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 Some mosses – Have conducting tissues in the center of their “stems” and may grow vertically

27. 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 Hornwort and moss sporophytes – Have stomata

28. 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

29. “Tolland Man,” a bog mummy dating from 405–100 B.C. The acidic, oxygen-poor conditions produced by Sphagnum canpreserve human or other animal bodies for thousands of years. Ecological and Economic Importance of Mosses Sphagnum, or “peat moss” – Forms extensive deposits of partially decayed organic material known as peat – Plays an important role in the Earth’s carbon cycle Gametophyte Sporangium at tip of sporophyte Living photo- synthetic cells Dead water- storing cells 100 µm Closeup of Sphagnum. Note the “leafy” gametophytes and their offspring, the sporophytes. (b) Sphagnum “leaf” (LM). The combination of living photosynthetic cells and dead water-storing cells gives the moss its spongy quality. (c) Peat being harvested from a peat bog (a) Figure 29.10 a–d (d)

30. Concept 29.4: Ferns and other seedless vascular plants formed the first forests Bryophytes and bryophyte-like plants – Were the prevalent vegetation during the first 100 million years of plant evolution Vascular plants – Began to evolve during the Carboniferous period

31. Origins and Traits of Vascular Plants Fossils of the forerunners of vascular plants – Date back about 420 million years

32. These early tiny plants – Had independent, branching sporophytes – Lacked other derived traits of vascular plants Figure 29.11

33. Life Cycles with Dominant Sporophytes In contrast with bryophytes – Tracheophytes- Vascular plants – Sporophytes of seedless vascular plants are the dominant generation, as in the familiar leafy fern – The gametophytes are tiny plants that grow on or below the soil surface – Remember- in mosses it is the gametophyte that is dominant

34. 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

35. Transport in Xylem and Phloem Vascular plants have two types of vascular tissue – Xylem and phloem – These carry water and foods (sugars) to various parts of the plant.

36. 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 – Phloem= food xylem=water

37. 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 – Roots are part of the vascular system

38. Evolution of Leaves Leaves – Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis

39. Leaves are categorized by two types – Microphylls, leaves with a single vein – Megaphylls, leaves with a highly branched vascular system

40. According to one model of evolution – Microphylls evolved first, as outgrowths of stems Vascular tissue Microphylls, such as those of lycophytes, may have originated as small stem outgrowths supported by single, unbranched strands of vascular tissue. (a) Megaphylls, which have branched vascular systems, may have evolved by the fusion of branched stems. (b) Figure 29.13a, b

41. 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

42. All seed plants and some seedless vascular plants – Are heterosporous, having two types of spores that give rise to male and female gametophytes

43. 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 (ptera= winged), names after the fern fronds as feathers

44. The 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

45. Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts Modern species of lycophytes – Are relics from a far more eminent past – Are small herbaceous plants

46. Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives Ferns – Are the most diverse seedless vascular plants

47. 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

48. 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 – We are still using the stored fuel from this period as energy