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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). Challenges of terrestriality • Dessication: medium of air, not water. • Access to water, nutrients. • Reproductive strategies. • Plants form the basis for every terrestrial ecosystem. Advantages of terrestriality • Ample, unfiltered sunlight • Abundant CO2 • Abundant soil nutrients • Initially no natural enemies (herbivores) 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 Important adaptations to life on land • Waxy cuticle • Gametangia and protected embryo • Roots (below) stems (above) • Leaves, stomata: photosynthesis 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 1 2/9/11 Major events in plant evolution Major events in plant evolution A. B. C. D. Changes in life history Vascular tissue Seeds Flowering plants Generalized Alternation of Generation in Plants 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. 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. 2 2/9/11 s te D. Flowering Plants: Angiosperms 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 • 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 Em yo s ar Ch s’ te o ry ‘B y ph o c Ly s s te y ph yte h op er Pt m Gy ed Va sc tis ula su r e br yo ios s te y ph o ar g An Ch s s rm pe s no Se Em s m r pe 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 An yo s s yte Flowers: Complex structure containing seeds within protective ovary. All descendants known as “Angiosperms” ar Ch s’ te h op o ry ‘B y ph o c Ly s s te y ph yte h op er Pt p ios g An Seeds: Embryo packed with a supply of nutrients inside a protective coat. All descendants known as “Spermatophytes” br m er p ios Va sc tis ula su r e s m er te hy Vascular tissue: Cells joined into tubes to transport water and soil nutrients upward (xylem) and carbohydrates downward (phloem). All descendants known as “Tracheophytes” br yte p ios Embryo: zygotes are retained within tissues of the female parent plant. All descendants known as “Embryophyta” te hy h op s m er te hy s rm pe s no m Gy 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. 3 2/9/11 BRYOPHYTES Mosses, Liverworts, Hornworts 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. KEY POINTS • Gametophyte dominant • No vascular tissue • Ancient but persistent group. Fig. 29.7 from textbook indicates that bryophytes are paraphyletic, however… Bryophytes 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. 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 4 2/9/11 Bryophytes Fig. 29-8-3 Bryophytes Raindrop Sperm Bryophyta: Mosses “Bud” Male gametophyte (n) Key • Best known of bryophytes Haploid (n) Diploid (2n) – Note that “bryophytes” is a term of convenience, where as Bryophyta is restricted to the mosses. Protonemata (n) Antheridia “Bud” Egg Spores • Small individual plants in tight packages--form spongy,supporting mats. • Anchor to substrate with rhizoids Gametophore Female Archegonia gametophyte (n) Spore dispersal Rhizoid Peristome FERTILIZATION Sporangium – “roots”, like “leaves” not homologous with vascular plants MEIOSIS Mature sporophytes • Life cycle good example of alternating generations Seta Capsule (sporangium) Foot Zygote (2n) (within archegonium) Embryo 2 mm Archegonium Capsule with peristome (SEM) Young sporophyte (2n) Female gametophytes Bryophytes Hepatophyta: Liverworts Anthocerophyta: Hornworts • Very inconspicuous, lobed bodies hugging ground • Life cycle like mosses • Thalloid form & Leafy form • Likely sister-group of remaining (all other) Plantae s yte ar Ch s’ te h op o ry ‘B y ph o c Ly • Resemble liverworts • Name derives from sporophytes in hornlike capsules of matlike gametophyte • Cells have a single large chloroplast s s te y ph yte h op er Pt Em br yo Bryophytes 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” 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. 5 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 Seedless Vascular Plants General Structure • Roots & shoots • Lignified vascular tissue: Xylem, Phloem • Some heterosporous – Megaspores (female) – Microspores (male) – As in seed plants Fern with characteristic macrophylls Megaspores Fern sperm with multiple flagellae Lycopod Selaginella Seedless Vascular Plants Seedless Vascular Plants Lycophyta: Lycopods Club mosses, quillworts, ground pines • Relicts of flourishing past, two lineages: • Only small forms extant Lycopodium Club moss or ground pine • Many are tropical epiphytes; temperate forms grow at ground level • Sporangia borne on sporophylls: leaves specialized for reproduction ph ro a Ch ‘ Relicts of flourishing past, two lineages: • Only small forms extant • Many are tropical epiphytes; temperate forms grow at ground level Sporangia borne on sporophylls: • c Ly yo m er sp no m Gy Va sc tis ula su r e br Seedless Vascular Plants s s yte es Em – leaves specialized for reproduction Isoetes Quillwort t hy ph op tero P t hy op y Br ’ es • – E.g. Lycopodium, Saleginella – E.g. Lycopodium, Saleginella s Lycophyta: Lycopods Club mosses, quillworts, ground pines – Giant, tree-like, woody – Small herbaceous – Giant, tree-like, woody – Small herbaceous yte Microspores pe ios s rm g An Pterophyta I: Horsetails • Previously considered own phylum, Sphenophyta, now placed within Pterophyta. • Late Paleozoic forms grew to 15m • Today only the genus Equisetum Note Pterophyta are sister to Spermatophyta: Megaphyll leaves, roots that can branch – 15 species mostly northern hemisphere • Conspicuous horsetail sporophyte • Homosporous…bisexual gametophyte An exception: Equisetum giganteum from Chile 6 2/9/11 Seedless Vascular Plants Pterophyta I: Horsetails 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 • Underground rhizome from which stems arise • Stems: hollow, jointed with whorls of small branches • Cone-like sporangia at tip of stem. LIFE CYCLE: sporophyte with specialized leaves, each with clustered sporangia below (sori) which launch spores, grow into gametophyte 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. Gymnosperms The CARBONIFEROUS • • • • and the Evolution of Seed Plants 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) 7 2/9/11 Seed Plants Key points • Seed replaces spore • Fertilization by pollen instead of sperm • Two groups: gymnosperms Gymnosperms: Conifers & Allies 1. Success marked by change in life cycle 2. Evolution 3. Four divisions – (naked seeds) • Angiosperms – (protected seeds) Changes in Life Cycle 1. Gametophyte highly reduced – Retained within reproductive tissue of sporophyte and not cast out as independent generation. – Shift toward diploidy. Changes in Life Cycle 2. Fertilization by pollen rather than swimming sperm. – There is no longer a reliance on water! Fig. 30-6-1 Changes in Life Cycle Key Haploid (n) Diploid (2n) Ovulate cone Pollen cone 3. Seed. – – – Zygote not independent Zygote to embryo packaged with food in a seed coat. Seed is “naked” born on scales of cones. • • Mature sporophyte (2n) Microsporocytes (2n) Pollen grains (n) MEIOSIS Microsporangia Microsporangium (2n) Protects from dessication. Increases dispersal capabilities: replaces spore as dispersal agent. 8 2/9/11 Fig. 30-6-4 Key Haploid (n) Diploid (2n) Evolution 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) Seedling Surviving megaspore (n) Archegonium Permian harshness (formation of Pangea) Interior aridity Demise of Carboniferous forests Female gametophyte Seeds Food reserves (n) Seed coat (2n) Embryo (2n) • 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) Mass Extinctions Sperm nucleus (n) Rise of Gymnosperms Pollen tube FERTILIZATION Egg nucleus (n) Four Divisions • Cycadophyta – Cycads • Ginkgophyta – Ginkgo • Gnetophyta – Gnetales • Coniferophyta – Conifers Ginkgophyta: Gingko • Diverse in Mesozoic, single species today • Known only from fossils until discovered growing in Chinese Buddhist temples 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 Gnetophyta • Gnetum: tropical tree/vine. • Ephedra: Mormon or Mexican tea of American deserts, jointed stem. • Fan-shaped, deciduous leaves • Male trees widely planted landscape tree • Welwitschia: Largest known leaves, deserts of SW Africa, deep root, exposed leaves. – Resistant to drought, pollution, pests • Seeds of female produce stench when crushed • Fossils from Permian, but peak diversity in Cretaceous. 9 2/9/11 Coniferophyta (or Pinophyta): Conifers 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? • 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 • • • • • • Summary: Gymnosperms 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 • 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) 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 Se Angiosperms Structure & Classification m Gy 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” 10 2/9/11 General Aspects KEY POINT • Flower and fruit as defining reproductive strategy 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 General Aspects Angiosperms • Vessel elements • Also present in Gnetales and absent from many basal angiosperm groups. • ??? Possibilities ??? • Specialized for transport, less for support 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 11 2/9/11 Morphology Morphology Roots Roots Anchor Shoot System Anchor Shoot System • Tap root • 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 – 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 – Mat-like and spreading, shallow, wide coverage – Grasses (good erosion control) Morphology Roots Roots Anchor Shoot System Anchor Shoot System • Root hairs: For absorption at root tip • Adventitious roots: above ground roots help support stem • 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 – Adventitious = Name for any plant part growing in abnormal place – Prop roots – Aerial roots Morphology Shoots Shoots Stems, leaves, flowers Stems, leaves, flowers • • • • • • Modified stems • Stolons Nodes Internodes Axillary buds Apex = terminal bud Apical dominance – Horizontal above-ground runners (e.g. strawberries) • Rhizomes – Horizontal below-ground stems (potatoes, iris) • Bulbs – Vertical below ground with leaves modified for storage. 12 2/9/11 Morphology Morphology Shoots Shoots Stems, leaves, flowers Stems, leaves, flowers • Modified stems • Stolons • Modified stems • Stolons – Horizontal above-ground runners (e.g. strawberries) • Rhizomes – Horizontal above-ground runners (e.g. strawberries) • Rhizomes – Horizontal below-ground stems (potatoes, iris) • Bulbs – Horizontal below-ground stems (potatoes, iris) • Bulbs – Vertical below ground with leaves modified for storage. Morphology – Vertical below ground with leaves modified for storage. Morphology Shoots Shoots Stems, leaves, flowers Stems, leaves, flowers • Primary photosynthetic part of plant (usually) • Part 1: Blade • Part 2: Petiole • Primary photosynthetic part of plant (usually) • Part 1: Blade • Part 2: Petiole – Absent in many grasses and relatives (monocots) Morphology – Absent in many grasses and relatives (monocots) Morphology Shoots Shoots Stems, leaves, flowers • Highly variable Stems, leaves, flowers • Highly variable – Within individuals – Between species – Between deeper clades • • • • • Shape Arrangement Margins Venation Simple vs Compound – Within individuals – Between species – Between deeper clades • • • • • Shape Arrangement Margins Venation Simple vs Compound 13 2/9/11 Morphology Morphology Shoots Shoots Stems, leaves, flowers • Highly variable Stems, leaves, flowers • Highly variable – Within individuals – Between species – Between deeper clades • • • • • Shape Arrangement Margins Venation Simple vs Compound Morphology – Within individuals – Between species – Between deeper clades • • • • • Shape Arrangement Margins Venation Simple vs Compound Morphology Shoots Shoots Stems, leaves, flowers • Highly variable Stems, leaves, flowers • Some can be highly modified: – Within individuals – Between species – Between deeper clades • • • • • – Tendrils – Spines – Storage – Asexual reproduction – Bracts – Insectivory Shape Arrangement Margins Venation Simple vs Compound Morphology Morphology Shoots Shoots Stems, leaves, flowers • Some can be highly modified: Stems, leaves, flowers • Some can be highly modified: – Tendrils – Spines – Storage – Asexual reproduction – Bracts – Insectivory – Tendrils – Spines – Storage – Asexual reproduction – Bracts – Insectivory Venus flytrap Sundew Pitcher plant 14 2/9/11 Morphology Morphology Shoots Shoots Stems, leaves, flowers Stems, leaves, flowers • Carpels are the female organs • Angiosperm structure specialized for sexual reproduction. • Specialized shoot made up of (usually) four rings of modified leaves (floral organs): – – – – – Ovules contain megasporangium – Stigma receives pollen – Style leads from stigma to ovary – Ovary contains ovules Sepals Petals Carpels: Female Anthers: Male Morphology Morphology Shoots Shoots Stems, leaves, flowers Stems, leaves, flowers • Stamens are the male organs • Perfect flowers contain both carpels and stamens • Imperfect flowers contain either carpels or stamens – Filament is the stalk – Anther houses microsporangia and produces pollen. – Pollen will contain male gametophyte – Monoecious: having separate male and female flowers on the same plant. – Dioecious: having separate male and female plants. Morphology Morphology Shoots Shoots Stems, leaves, flowers 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) 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 Water lily, Nymphaceae, showing plesiomorphic state Morning glory, showing derived state 15 2/9/11 Morphology Morphology Shoots Shoots Stems, leaves, flowers 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) 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 Major Angiosperm Dichotomy • Monocots and Dicots • Refers to numbers of “seed leaves” or cotyledons. • Monocots are monophyletic. • Dicots are NOT. Major Angiosperm Dichotomy Monocots: Grasses, lilies, palms, etc. Dicots: Everything else • Monocots and Dicots • Refers to numbers of “seed leaves” or cotyledons. • Monocots are monophyletic. • Dicots are NOT. Major Angiosperm Dichotomy Major Angiosperm Dichotomy • Monocots and Dicots • Refers to numbers of “seed leaves” or cotyledons. • Monocots are monophyletic. • Dicots are NOT. • Monocots and Dicots • Refers to numbers of “seed leaves” or cotyledons. • Monocots are monophyletic. • Dicots are NOT. • “Dicot is a term of convenience. 16 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? 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 17 2/9/11 Life Forms Life Forms • Grasses • Forbs • Shrubs – Woody tissue – No distinct single trunk • • • • • Trees Epiphytes Aquatic Herbaceous Woody • • • • 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 Grasses Forbs Shrubs Trees Epiphytes Aquatic – Numerous adaptations for living in water • Herbaceous • Woody • • • • • Grasses Forbs Shrubs Trees Epiphytes – Plant that grows on another plant • Aquatic • Herbaceous • Woody Life Forms • • • • • • Life Forms 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. 18 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. 19