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Plants Colonized Land

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  1. Plants Colonized Land

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

  3. Morphological and Biochemical Evidence • Land plants share key traits only with charophyceans: • Peroxisome enzymes • Structure of flagellated sperm • Chlorophyll A

  4. Viridiplantae Streptophyta Plantae Charophyceans Red algae Embryophytes Chlorophytes Ancestral alga

  5. Derived Traits of Plants • Five key traits appear in nearly all land plants but are absent in the green algae: • Apical meristems • Alternation of generations • Walled spores produced in sporangia-aexual reproduction • Multicellular gametangia-gamete producing structures • Multicellular dependent embryos

  6. Apical Meristems Apical Meristem of shoot Developing leaves Apical meristem Shoot Root 100 µm 100 µm

  7. Alternation of Generations Haploid multicellular organism (gametophyte) Mitosis Mitosis Gametes Spores MEIOSIS FERTILIZATION Zygote Mitosis Diploid multicellular organism (sporophyte)

  8. 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

  9. 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). Fossilized sporophyte tissue. The spores were embedded in tissue that appears to be from plants.

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. MOSS SPOROPHYTE

  16. MOSS GAMETOPHYTE

  17. Polytrichum commune, hairy cap moss Sporophyte LE 29-9d Gametophyte

  18. 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)

  19. 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)

  20. LIVERWORT STRUCTURE

  21. GEMMA CUPS

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

  23. Ecological and Economic Importance of Mosses • Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat • Sphagnum plays an important role in the Earth’s carbon cycle

  24. LE 29-10 A peat bog. 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. Sphagnum “leaf” (LM). The combination of living photosynthetic cells and dead water-storing cells gives the moss its spongy quality. “Tolland Man,” a bog mummy dating from 405–100 B.C. The acidic, oxygen-poor conditions produced by Sphagnum can preserve human or animal bodies for thousands of years.

  25. 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 diversify during the Carboniferous period • Vascular plants dominate most landscapes today

  26. Origins and Traits of Vascular Plants • Fossils of the forerunners of vascular plants date back about 420 million years • , branching sporophytes • They lacked other derived These early tiny plants had independent traits of vascular plants

  27. 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

  28. Key Haploid (n) Diploid (2n) Antheridium Spore Young gametophyte MEIOSIS LE 29-12 Sporangium Sperm Archegonium Egg New sporophyte Mature sporophyte Sporangium Zygote FERTILIZATION Sorus Gametophyte Fiddlehead

  29. 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

  30. 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

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

  32. 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

  33. Vascular tissue LE 29-13 Microphylls Megaphylls

  34. 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 • Allseed plants and some seedless vascular plants are heterosporous, having two types of spores that give rise to male and female gametophytes

  35. Classification of Seedless Vascular Plants • There are two phyla of seedless vascular plants: • Lycophyta includes club mosses, spike mosses, and quillworts • Pterophyta includes ferns, horsetails, and whisk ferns and their relatives

  36. Selaginella apoda, a spike moss LE 29-14a

  37. LE 29-14b Isoetes gunnii, a quillwort

  38. Strobili (clusters of sporophyllis) LE 29-14c Diphasiastrum tristachyum, a club moss

  39. Psilotum nudum, a whisk fern LE 29-14d

  40. Equisetum arvense, field horsetail LE 29-14e Vegetative stem Strobilus on fertile stem

  41. LE 29-14f Athyrium filix-femina, lady fern

  42. Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives • Ferns are the most diverse seedless vascular plants, with more than 12,000 species • They are most diverse in the tropics but also thrive in temperate forests • Some species are even adapted to arid climates

  43. 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 • These forests may have helped produce the global cooling at the end of the Carboniferous period • The decaying plants of these Carboniferous forests eventually became coal