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Transcript
2/9/11 Plants • Key point: History of land plants is the increasing adaptation to terrestriality. • Colonized land 475 mya (Ordovician), began growing taller 370 mya (Carboniferous). • Plants form the basis for every terrestrial ecosystem. Challenges of terrestriality • Dessication: medium of air, not water. • Access to water, nutrients. • Reproductive strategies. Advantages of terrestriality • Ample, unfiltered sunlight • Abundant CO2 • Abundant soil nutrients • Initially no natural enemies (herbivores) 1 2/9/11 Important adaptations to life on land • Waxy cuticle • Gametangia and protected embryo • Roots (below) stems (above) • Leaves, stomata: photosynthesis Origins: Charophyte Green Algae EVIDENCE • Homologous chloroplasts • Biochemical similarity: cellulose in cell wall • Similarity in mitosis, cytokinesis • Similarity in sperm ultrastructure • Genetic relationship: some nuclear genes, ribosomal RNA Origins: Charophyte Green Algae ESSENTIAL DIFFERENCES Green Algae Plants Medium: water (whole alga has access) Medium: air, nonsupportive (roots, stiff stem, cuticle) Photosynthesis in most cells (light limited) Photosynthesis in aerial parts (leaves, stomata) Reproduction mostly asexual Reproduction sexual: gametangia, embryo 2 2/9/11 Major events in plant evolution A. B. C. D. Changes in life history Vascular tissue Seeds Flowering plants Major events in plant evolution A. Changes in life history “The changes that affect an organism’s schedule of reproduction and survival.” 1. Alternation of generations – Evolved independently in fungi, cellular slime molds, brown algae, red algae, and green algae. Generalized Alternation of Generation in Plants 3 2/9/11 Major events in plant evolution A. Changes in life history 2. Generations are heteromorphic. 3. Shift of dominance from gametophyte (n) to sporophyte (2n). 4. Replacement of flagellated sperm by pollen. B. Vascular tissue • Cells joined into conducting tubes. • Xylem: dead, lignified tubes conduct water, mineral from roots upward. • Phloem: living tubes conduct sugar, amino acids from photosythetic parts downward. C. Seeds • An embryo packed with food. • First seeds unencapsulated Gymnosperms. 4 2/9/11 D. Flowering Plants: Angiosperms • Complex structure containing seeds within protective ovary. • Most diverse (species) plant group. s te y ph o ar Ch s s’ m s s te er yte phy sp h o p o n op m co ter ry P Ly Gy ‘B s m er te hy p ios g An Embryo: zygotes are retained within tissues of the female parent plant. All descendants known as “Embryophyta” s yte ar Ch s’ te h op o ry ‘B y ph o c Ly s s te y ph yte h op er Pt Em br yo m Gy s rm pe s no s m er p ios g An Vascular tissue: Cells joined into tubes to transport water and soil nutrients upward (xylem) and carbohydrates downward (phloem). All descendants known as “Tracheophytes” 5 2/9/11 s te y ph ro a Ch s s’ m s s er te yte sp hy oph o p p n o m co ter ry P Ly Gy ‘B Va sc tis ula su r e Em yo s te o ar Ch g An s s’ m s s te er yte phy sp h o p o n op m co ter ry P Ly Gy ‘B Em g Flowers: Complex structure containing seeds within protective ovary. All descendants known as “Angiosperms” s br yo s yte ar s’ te h op o ry ‘B y ph o c Ly s s te y ph yte h op er Pt s rm pe s no m Gy p ios An ed Va sc tis ula su r e s m er te hy Se Ch p ios Seeds: Embryo packed with a supply of nutrients inside a protective coat. All descendants known as “Spermatophytes” br y ph s m er te hy s m er p ios g Fl An ow er s Se ed Em Va sc tis ula su r e br yo s Increasing Terrestriality Key point: History of land plants is the increasing adaptation to terrestriality. 6 2/9/11 BRYOPHYTES Mosses, Liverworts, Hornworts KEY POINTS • Gametophyte dominant • No vascular tissue • Ancient but persistent group. BRYOPHYTES Mosses, Liverworts, Hornworts • Not monophyletic (???) • Date to > 475 mya • Very successful, 24,000 species, but never dominated landscape. • Non-vascular; therefore only found in moist environments. • Need water for sperm transport and absorption. Fig. 29.7 from textbook indicates that bryophytes are paraphyletic, however… BRYOPHYTES Mosses, Liverworts, Hornworts • Not monophyletic (???) • Date to > 475 mya • Very successful, 24,000 species, but never dominated landscape. • Non-vascular; therefore only found in moist environments. • Need water for sperm transport and absorption. 7 2/9/11 Bryophytes Common Characteristics • Gametophyte generation dominates • Lack stiff, supporting structures – Therefore low-growing • Separate male and female gametophyte – Male gametangium = antheridium (flagellated sperm cells) – Female gametangium = archegonium (single egg) • Fertilization within archegonium -> zygote -> embryo Bryophytes Common Characteristics • Gametophyte generation dominates • Lack stiff, supporting structures – Therefore low-growing • Separate male and female gametophyte – Male gametangium = antheridium (flagellated sperm cells) – Female gametangium = archegonium (single egg) • Fertilization within archegonium -> zygote -> embryo Bryophytes Common Characteristics • Gametophyte generation dominates • Lack stiff, supporting structures – Therefore low-growing • Separate male and female gametophyte – Male gametangium = antheridium (flagellated sperm cells) – Female gametangium = archegonium (single egg) • Fertilization within archegonium zygote embryo 8 2/9/11 Bryophytes Bryophyta: Mosses • Best known of bryophytes – Note that “bryophytes” is a term of convenience, where as Bryophyta is restricted to the mosses. • Small individual plants in tight packages--form spongy,supporting mats. • Anchor to substrate with rhizoids – “roots”, like “leaves” not homologous with vascular plants • Life cycle good example of alternating generations Fig. 29-8-3 Bryophytes Raindrop Sperm “Bud” Male gametophyte (n) Key Haploid (n) Diploid (2n) Protonemata (n) Antheridia “Bud” Egg Spores Gametophore Female Archegonia gametophyte (n) Spore dispersal Rhizoid Peristome FERTILIZATION Sporangium MEIOSIS Mature sporophytes Seta Capsule (sporangium) Foot Zygote (2n) (within archegonium) Embryo 2 mm Archegonium Capsule with peristome (SEM) Young sporophyte (2n) Female gametophytes Bryophytes Hepatophyta: Liverworts • Very inconspicuous, lobed bodies hugging ground • Life cycle like mosses • Thalloid form & Leafy form • Likely sister-group of remaining (all other) Plantae 9 2/9/11 Bryophytes Anthocerophyta: Hornworts • Resemble liverworts • Name derives from sporophytes in hornlike capsules of matlike gametophyte • Cells have a single large chloroplast s te o ar Ch y ph s s’ m s s te er yte phy sp h o p o n op m co ter ry P Ly Gy ‘B Em br yo p ios s m er te hy g An Vascular tissue: Cells joined into tubes to transport water and soil nutrients upward (xylem) and carbohydrates downward (phloem). All descendants known as “Tracheophytes” Seedless Vascular Plants Lycophytes & Pterophytes KEY POINTS • Plants with xylem and phloem • Branched sporophyte dominates • Ancestral state retains flagellated sperm and thus inhabit moist environments • Paraphyletic • “Vascular plant” monophyletic: Tracheophyta. 10 2/9/11 Seedless Vascular Plants General Macroevolution Lycopod with microphylls shown • Earliest are found in mid-Paleozoic, 425 mya (e.g. Cooksonia) • Dominated landscape by end of paleozoic • Branched sporophyte dominant generation • All with flagellated sperm Fern with characteristic macrophylls Fern sperm with multiple flagellae Seedless Vascular Plants General Structure • Roots & shoots • Lignified vascular tissue: Xylem, Phloem • Some heterosporous – Megaspores (female) – Microspores (male) – As in seed plants Megaspores Microspores Lycopod Selaginella Seedless Vascular Plants Lycophyta: Lycopods Club mosses, quillworts, ground pines • Relicts of flourishing past, two lineages: – Giant, tree-like, woody – Small herbaceous • Only small forms extant – E.g. Lycopodium, Saleginella • Many are tropical epiphytes; temperate forms grow at ground level • Sporangia borne on sporophylls: leaves specialized for reproduction Lycopodium Club moss or ground pine Isoetes Quillwort 11 2/9/11 Seedless Vascular Plants Lycophyta: Lycopods Club mosses, quillworts, ground pines • Relicts of flourishing past, two lineages: – Giant, tree-like, woody – Small herbaceous • Only small forms extant • Many are tropical epiphytes; temperate forms grow at ground level Sporangia borne on sporophylls: – E.g. Lycopodium, Saleginella • – leaves specialized for reproduction s te o ar Ch y ph s s’ m s s te er yte phy sp h o p o n op m co ter ry P Ly Gy ‘B Va sc tis ula su r e Em br yo p ios s m er te hy g An Note Pterophyta are sister to Spermatophyta: Megaphyll leaves, roots that can branch Seedless Vascular Plants Pterophyta I: Horsetails • Previously considered own phylum, Sphenophyta, now placed within Pterophyta. • Late Paleozoic forms grew to 15m • Today only the genus Equisetum – 15 species mostly northern hemisphere • Conspicuous horsetail sporophyte • Homosporous…bisexual gametophyte An exception: Equisetum giganteum from Chile 12 2/9/11 Seedless Vascular Plants Pterophyta I: Horsetails • Underground rhizome from which stems arise • Stems: hollow, jointed with whorls of small branches • Cone-like sporangia at tip of stem. Seedless Vascular Plants Pterophyta II: True ferns • Most diverse seedless vascular plants • Today ~12,000 species • Most diversity in tropics, also common in temperate regions. • Fronds are large leaves with branched veins: megaphyll • Compound leaflets grow from fiddlehead tip • Leaves may sprout directly from prostrate stems (rhizomes); or as upright treeferns LIFE CYCLE: sporophyte with specialized leaves, each with clustered sporangia below (sori) which launch spores, grow into gametophyte 13 2/9/11 Pterophyta II: Whiskferns • Previously considered own phylum, Psilophyta, now placed within Pterophyta. • Simple plants. • Diploid sporophyte has dichotomous branches (like primitive Cooksonia) • True roots and leaves are absent – Like Lycopods! However, these have been secondarily lost. The CARBONIFEROUS • • • • 360-300 mya Height of seedless vascular diversity and ecological dominance. Formed first forests. Eventually become COAL: – Dead plants did not completely decay. – Became peat bogs. – Eventually covered by sea. – Heat and pressure from sediments converted peat to coal. 4 square miles of Carboniferous coal forest in Pennsylvania (see http://www.mnh.si.edu/highlight/riola/ for highlights) Gymnosperms and the Evolution of Seed Plants 14 2/9/11 Seed Plants Key points • Seed replaces spore • Fertilization by pollen instead of sperm • Two groups: gymnosperms – (naked seeds) • Angiosperms – (protected seeds) Gymnosperms: Conifers & Allies 1. Success marked by change in life cycle 2. Evolution 3. Four divisions Changes in Life Cycle 1. Gametophyte highly reduced – Retained within reproductive tissue of sporophyte and not cast out as independent generation. – Shift toward diploidy. 15 2/9/11 Changes in Life Cycle 2. Fertilization by pollen rather than swimming sperm. – There is no longer a reliance on water! Changes in Life Cycle 3. Seed. – – – Zygote not independent Zygote to embryo packaged with food in a seed coat. Seed is “naked” born on scales of cones. • • Protects from dessication. Increases dispersal capabilities: replaces spore as dispersal agent. Fig. 30-6-1 Key Haploid (n) Diploid (2n) Ovulate cone Pollen cone Mature sporophyte (2n) Microsporocytes (2n) Pollen grains (n) MEIOSIS Microsporangia Microsporangium (2n) 16 2/9/11 Fig. 30-6-4 Key Haploid (n) Diploid (2n) Ovule Ovulate cone Pollen cone Integument Megasporocyte (2n) Microsporocytes (2n) Megasporangium Pollen (2n) Pollen grain grains (n) MEIOSIS MEIOSIS Mature sporophyte (2n) Microsporangia Microsporangium (2n) Surviving megaspore (n) Seedling Archegonium Female gametophyte Seeds Food reserves (n) Seed coat (2n) Embryo (2n) Sperm nucleus (n) Pollen tube FERTILIZATION Egg nucleus (n) Evolution • Appear much earlier than Angiosperms, in Devonian. “Modern” gymnosperms by early-mid Mesozoic • Permian marks end of Paleozoic. • Mesozoic: Age of Dinosaurs (zoologists); Age of Gymnosperms (botanists) Permian harshness (formation of Pangea) Interior aridity Demise of Carboniferous forests Mass Extinctions Rise of Gymnosperms Four Divisions • Cycadophyta – Cycads • Ginkgophyta – Ginkgo • Gnetophyta – Gnetales • Coniferophyta – Conifers 17 2/9/11 Cycadophyta: Cycads • Cycads or “Sago” palm • Currently ~130 species – Slow-growing, tropical & subtropical • Flourished in Mesozoic • Massive cone-shaped structures bearing pollen or ovules • Primarily insect pollinated, some wind pollinated. • Seeds eaten in Asia after removing Alkaloids Ginkgophyta: Gingko • Diverse in Mesozoic, single species today • Known only from fossils until discovered growing in Chinese Buddhist temples • Fan-shaped, deciduous leaves • Male trees widely planted landscape tree – Resistant to drought, pollution, pests • Seeds of female produce stench when crushed Gnetophyta • Gnetum: tropical tree/vine. • Ephedra: Mormon or Mexican tea of American deserts, jointed stem. • Welwitschia: Largest known leaves, deserts of SW Africa, deep root, exposed leaves. • Fossils from Permian, but peak diversity in Cretaceous. 18 2/9/11 Gnetophyta • Have vessel elements: Differ from all other Gymnosperms, share this with Angiosperms. • What are the implications if Gymnosperms are monophyletic? • What are the implications if vessel elements are homologous? Coniferophyta (or Pinophyta): Conifers • Pines, firs, spruce, larches, cedars, hemlocks, (all Pinaceae), yews, cypress, redwoods, hoop pines, umbrella pines, yellowwoods, plum-yews. • ~600 species, dominate vast regions of taiga: northern and southern evergreen forests. Coniferophyta (or Pinophyta): Conifers • • • • • • Evergreen, even perform limited photosynthesis year round. Needles are leaves Commercially important as timber Tallest plant: coastal redwood (>110m) Heaviest plant: giant sequoia (2500 metric tons) Oldest plant: Bristlecone pine >4600 years old 19 2/9/11 Summary: Gymnosperms • Monophyletic sister group to angiosperms. • Peak diversity in the Mesozoic, still ecologically dominant in some ecosystems. • Evolution of seed and pollen key transitions (shared with Angiosperms) Angiosperms Structure & Classification s yte ar Ch s’ te h op o ry ‘B y ph o c Ly s s te y ph yte h op er Pt m Gy Se ed Em Va sc tis ula su r e br yo s s rm pe s no s m er p ios g An Flowers: Complex structure containing seeds within protective ovary. All descendants known as “Angiosperms” 20 2/9/11 KEY POINT • Flower and fruit as defining reproductive strategy General Aspects Angiosperms • Anthophyta: “flower plant” • 270,000 described species. – Compare this to ~900 species of Gymnosperms! General Aspects Angiosperms • Refined vascular tissue • Vessel elements present in xylem – shorter, wider cells placed end to end – perforation plates at end of each cell – line up end-to-end to create vessels • Specialized for transport, less for support 21 2/9/11 General Aspects Angiosperms • Vessel elements • Also present in Gnetales and absent from many basal angiosperm groups. • ??? Possibilities ??? General Aspects Angiosperms • Of course… • Characterized by flowers • Characterized by fleshy ovary protecting seed Morphology Two Systems • Roots: below-ground non-photosynthetic – Anchor – Absorption – Storage • Aerial shoots: aboveground photosynthetic and/or transport – Leaves – Stems • These are interdependent 22 2/9/11 Morphology Roots Anchor Shoot System • Tap root – Single large verticle root with secondary rootlets – Firm anchor – Food storage used by plant when producing flower, fruit (harvest before flowering) • Fibrous root – Mat-like and psreading, shallow, wide coverage – Grasses (good erosion control) Morphology Roots Anchor Shoot System • Tap root – Single large verticle root with secondary rootlets – Firm anchor – Food storage used by plant when producing flower, fruit (harvest before flowering) • Fibrous root – Mat-like and spreading, shallow, wide coverage – Grasses (good erosion control) Morphology Roots Anchor Shoot System • Root hairs: For absorption at root tip • Adventitious roots: above ground roots help support stem – Adventitious = Name for any plant part growing in abnormal place – Prop roots – Aerial roots 23 2/9/11 Morphology Roots Anchor Shoot System • Root hairs: For absorption at root tip • Adventitious roots: above ground roots help support stem – Adventitious = Name for any plant part growing in abnormal place – Prop roots – Aerial roots Morphology Shoots Stems, leaves, flowers • • • • • Nodes Internodes Axillary buds Apex = terminal bud Apical dominance Morphology Shoots Stems, leaves, flowers • Modified stems • Stolons – Horizontal above-ground runners (e.g. strawberries) • Rhizomes – Horizontal below-ground stems (potatoes, iris) • Bulbs – Vertical below ground with leaves modified for storage. 24 2/9/11 Morphology Shoots Stems, leaves, flowers • Modified stems • Stolons – Horizontal above-ground runners (e.g. strawberries) • Rhizomes – Horizontal below-ground stems (potatoes, iris) • Bulbs – Vertical below ground with leaves modified for storage. Morphology Shoots Stems, leaves, flowers • Modified stems • Stolons – Horizontal above-ground runners (e.g. strawberries) • Rhizomes – Horizontal below-ground stems (potatoes, iris) • Bulbs – Vertical below ground with leaves modified for storage. Morphology Shoots Stems, leaves, flowers • Primary photosynthetic part of plant (usually) • Part 1: Blade • Part 2: Petiole – Absent in many grasses and relatives (monocots) 25 2/9/11 Morphology Shoots Stems, leaves, flowers • Primary photosynthetic part of plant (usually) • Part 1: Blade • Part 2: Petiole – Absent in many grasses and relatives (monocots) Morphology Shoots Stems, leaves, flowers • Highly variable – Within individuals – Between species – Between deeper clades • • • • • Shape Arrangement Margins Venation Simple vs Compound Morphology Shoots Stems, leaves, flowers • Highly variable – Within individuals – Between species – Between deeper clades • • • • • Shape Arrangement Margins Venation Simple vs Compound 26 2/9/11 Morphology Shoots Stems, leaves, flowers • Highly variable – Within individuals – Between species – Between deeper clades • • • • • Shape Arrangement Margins Venation Simple vs Compound Morphology Shoots Stems, leaves, flowers • Highly variable – Within individuals – Between species – Between deeper clades • • • • • Shape Arrangement Margins Venation Simple vs Compound Morphology Shoots Stems, leaves, flowers • Highly variable – Within individuals – Between species – Between deeper clades • • • • • Shape Arrangement Margins Venation Simple vs Compound 27 2/9/11 Morphology Shoots Stems, leaves, flowers • Some can be highly modified: – Tendrils – Spines – Storage – Asexual reproduction – Bracts – Insectivory Morphology Shoots Stems, leaves, flowers • Some can be highly modified: – Tendrils – Spines – Storage – Asexual reproduction – Bracts – Insectivory Morphology Shoots Stems, leaves, flowers • Some can be highly modified: – Tendrils – Spines – Storage – Asexual reproduction – Bracts – Insectivory Venus flytrap Sundew Pitcher plant 28 2/9/11 Morphology Shoots Stems, leaves, flowers • Angiosperm structure specialized for sexual reproduction. • Specialized shoot made up of (usually) four rings of modified leaves (floral organs): – – – – Sepals Petals Carpels: Female Anthers: Male Morphology Shoots Stems, leaves, flowers • Carpels are the female organs – Ovules contain megasporangium – Stigma receives pollen – Style leads from stigma to ovary – Ovary contains ovules Morphology Shoots Stems, leaves, flowers • Stamens are the male organs – Filament is the stalk – Anther houses microsporangia and produces pollen. – Pollen will contain male gametophyte 29 2/9/11 Morphology Shoots Stems, leaves, flowers • Perfect flowers contain both carpels and stamens • Imperfect flowers contain either carpels or stamens – Monoecious: having separate male and female flowers on the same plant. – Dioecious: having separate male and female plants. Morphology Shoots Stems, leaves, flowers Evolutionary Trends 1. Reduction in number of floral parts 2. Floral parts fused, compound carpels to single and large 3. From radial to bilateral symmetry 4. Ovary drops below petals and sepals (“inferior” ovary) Water lily, Nymphaceae, showing plesiomorphic state Orchid, showing derived state Morphology Shoots Stems, leaves, flowers Evolutionary Trends 1. Reduction in number of floral parts 2. Floral parts fused, compound carpels to single and large 3. From radial to bilateral symmetry 4. Ovary drops below petals and sepals (“inferior” ovary) Water lily, Nymphaceae, showing plesiomorphic state Morning glory, showing derived state 30 2/9/11 Morphology Shoots Stems, leaves, flowers Evolutionary Trends 1. Reduction in number of floral parts 2. Floral parts fused, compound carpels to single and large 3. From radial to bilateral symmetry 4. Ovary drops below petals and sepals (“inferior” ovary) Water lily, Nymphaceae, showing plesiomorphic state Pea flower, showing derived state Morphology Shoots Stems, leaves, flowers Evolutionary Trends 1. Reduction in number of floral parts 2. Floral parts fused, compound carpels to single and large 3. From radial to bilateral symmetry 4. Ovary drops below petals and sepals (“inferior” ovary) Major Angiosperm Dichotomy • Monocots and Dicots • Refers to numbers of “seed leaves” or cotyledons. • Monocots are monophyletic. • Dicots are NOT. Monocots: Grasses, lilies, palms, etc. Dicots: Everything else 31 2/9/11 Major Angiosperm Dichotomy • Monocots and Dicots • Refers to numbers of “seed leaves” or cotyledons. • Monocots are monophyletic. • Dicots are NOT. Major Angiosperm Dichotomy • Monocots and Dicots • Refers to numbers of “seed leaves” or cotyledons. • Monocots are monophyletic. • Dicots are NOT. Major Angiosperm Dichotomy • Monocots and Dicots • Refers to numbers of “seed leaves” or cotyledons. • Monocots are monophyletic. • Dicots are NOT. • “Dicot is a term of convenience. 32 2/9/11 Dicots & Monocots • But it is a useful distinction… Dicots & Monocots • But it is a useful distinction… Dicots & Monocots • Discussion question: • For these traits, which are plesiomorphic and which are apomorphic? 33 2/9/11 Life Forms • Plant forms have evolved to fill numerous ecological roles or “niches”. • Developmental plasticity and Indeterminate growth allow individuals to fit particular ecological conditions. • Why is this so important to a plant? Life Forms • Grasses – – – – • • • • • • • Monocots No petiole Limited branching No woody tissue (herbaceous) Forbs Shrubs Trees Epiphytes Aquatic Herbaceous Woody Life Forms • Grasses • Forbs – Dicots – Generally wildflowers – Herbaceous • • • • • • Shrubs Trees Epiphytes Aquatic Herbaceous Woody 34 2/9/11 Life Forms • Grasses • Forbs • Shrubs – Woody tissue – No distinct single trunk • • • • • Trees Epiphytes Aquatic Herbaceous Woody Life Forms • • • • Grasses Forbs Shrubs Trees – Woody tissue – Single main trunk – Apical dominance pronounced • • • • Epiphytes Aquatic Herbaceous Woody Life Forms • • • • Grasses Forbs Shrubs Trees – Woody tissue – Single main trunk – Apical dominance pronounced • • • • Epiphytes Aquatic Herbaceous Woody 35 2/9/11 Life Forms • • • • • Grasses Forbs Shrubs Trees Epiphytes – Plant that grows on another plant • Aquatic • Herbaceous • Woody Life Forms • • • • • • Grasses Forbs Shrubs Trees Epiphytes Aquatic – Numerous adaptations for living in water • Herbaceous • Woody Life Forms • • • • • • • Grasses Forbs Shrubs Trees Epiphytes Aquatic Herbaceous – Die down each year. – Can be annual to perennial. – No structural lignin • Woody – Perennial and persistent – Structural lignin (wood) • Dichotomy used in above distinctions. 36 2/9/11 Summary • Flowering plants have been very successful: innovation of flower & fruit. • Diverse morphology structured around the root system and the shoot system. • Developmental plasticity and evolution of different life forms important in colonization of novel ecological niches. 37