Flowers

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Flowers

  1. 1. Flowers • Extraordinary diversity of color, size, form • Universal in objective – sexual reproduction for a rooted, stationary land plant! • 88% of all known plant species are flowering plants (260,000)
  2. 2. Flowering plants first appeared around 140 million years ago (Upper Jurassic). At that time the dominant forms of plant life were gymnosperms, cycads (at left), and ferns. Oldest flower fossil is 125 million years old. Flowers: A Marvelous Innovation Slide text from: http://herbarium.usu.edu/Teaching/bio2410/FLOWERS.ppt
  3. 3. Flowers dominate (except…) • Success of the flower as a repro. strategy makes it the dominant plant of the warmer lats • In far north or high altitudes, we see gymnosperms (like fir, spruce) remain http://www.uwsp.edu/geo/faculty/ritter/geog101/modules/natural_vegetation_of_north_america_map.html
  4. 4. Alternation of Generations
  5. 5. Why has the flower been such a success? • Protection • Pollination • Dispersal • Endosperm • Evolutionary possibility – adaptive radiation
  6. 6. Protection • Fruit helps prevent seed predation, resist dessication, may allow some seeds to last decades before germinating
  7. 7. Pollination • Often deliberate, targeted, effective means of delivering gametes to target!
  8. 8. Dispersal • Animal dispersed fruits, wind-dispersed seeds rely on evolved fruit forms – modifications of ovary not possible in non-flowering plants.
  9. 9. Endosperm • Nutritive tissue derived from unique fertilization events – provides early energy reserves for embryo
  10. 10. Possibility • Many specializations possible to modify original form
  11. 11. Four floral whorls • a calyx of sepals • a corolla of petals (alternative to above two, a perianth of tepals) • an androecium of stamens • a gynoecium of carpels
  12. 12. Calyx – The sepals • Often green, but not always • Frequently symmetric, in same number as petals • Occasionally becomes a modified capsule that encloses fruit – tomatillo!
  13. 13. Corolla – The petals • Note violet corolla of fused petals extending from a calyx of fused sepals in Datura!
  14. 14. Androecium – the stamens • Anther held on extending filament • May be attached to hypanthium or fused to petals
  15. 15. Androecium Solandra maxima K5 C5 A5 G2
  16. 16. Gynoecium – The carpels • Fused style branches of multiple carpels may appear as a single central structure http://www.csdl.tamu.edu/FLORA/imaxxgen.htm
  17. 17. Stamen and Stigma Alstroemeria aurantiaca D. Don ex Sweet; photos Dan Zimmerman, FCS Flower courtesy of Dr. Melinda Yin
  18. 18. Floral Formula - KCAG • K (or CA) Calyx • C (or CO) Corolla • A Androecium • G Gynoecium http://www.howe.k12.ok.us/~jimaskew/botzo/botforms.htm
  19. 19. Actinomorphic and Zygomorphic •Actinomorphic http://www.life.uiuc.edu/plantbio/260/Flowers/FloralTerms.html zygomorphic http://www.plantzafrica.com/plantnop/orchids/whatisorchid.htm
  20. 20. Jewelweed, Impatiens capensis Meerb.
  21. 21. Flower form - sympetaly http://www.missouriplants.com/Redalt/Im patiens_capensis_page.html Sympetaly = fused petals/tubular corolla
  22. 22. Zygomorphic Salvia patens Lamiaceae Salvia flower, FCS Morris Arboretum Trip, October 13, 2007
  23. 23. Mints - Lamiaceae http://www.eeob.iastate.edu/classes/botany306/terminology/flower/flowers.html Hypogynous flower implies superior ovary
  24. 24. Perfect and Imperfect flowers Begonia - imperfect carpellate staminate http://www.botany.hawaii.edu/faculty/webb/BOT410/Angiosperm/FlowerCompletePe Perfect Hosta
  25. 25. Cucurbitaceae • Imperfect flowers
  26. 26. Monoecious plant, staminate and carpellate (imperfect) flowers • Note the inferior ovary here
  27. 27. Pollination • Technically, pollination is simply the transfer of species- appropriate pollen to the receptive part of a flower. • Could be self- pollination (selfing) or cross-pollination (outcrossing) http://ecs.lewisham.gov.uk/youthspace/ca/webpagesf/pollination.jpg
  28. 28. Many possible vehicles for pollination • Wind • Insects (many different groups!) • Birds • Bats • A few other mammals Photographic database
  29. 29. Butterflies – vision & color http://webexhibits.org/causesofcolor/17C.html
  30. 30. Butterflies are great learners • Butterflies, whose color vision detects more wavelengths than either humans' or bees', can also associate colors with rewards. In one of the more dramatic experiments, cabbage butterflies learned a color with beelike speed -- after just one experience with a reward. Given a choice of two colors, the butterflies picked the rewarding hue 82 percent of the time, reported Alcinda C. Lewis of Boulder, Colo., and a colleague in Insect- Plant Interactions (CRC Press, Boca Raton, Fla., 1990). Pipevine swallowtails learned a preference for yellow or magenta within 10 visits to treat-laden flowers, reported Weiss in the May 1997 Animal Behaviour. • The butterflies could also keep two learned colors in mind for different purposes, Weiss says. She and Daniel R. Papaj of the University of Arizona have trained female pipevines to associate one color with sources of nectar and another with suitable spots for laying eggs.http://www.sciencenews.org/pages/sn_arc98/4_11_98/bob1.htm
  31. 31. Nectar guides – visible or UV
  32. 32. Moth pollinators
  33. 33. • In a famous example, Darwin described an orchid from Madagascar that had a foot-deep nectar well that kept the sweet liquid far out of reach of all known butterflies and moths. But the existence of the flower led him to predict the existence of a specialized moth with a foot-long proboscis that, like a straw, could reach the deep reward. Indeed, after Darwin’s death, researchers discovered just such an insect, and named it the “Predicta moth” in honor of Darwin’s educated guess.
  34. 34. Isabel Friedman, Apis mellifera on Asteraceae, Morris Arboretum October 13, 2007
  35. 35. Bees are important pollinators • Bees’ bodies well adapted to receive, transfer pollen • Bees’ vision includes UV spectral regions, but bees do not distinguish red as a visible color • Red-colored flowers are often bird- pollinated and not adapted for bees (poinsettia, hibiscus, red-flowered sages)
  36. 36. Colony Collapse Disorder? • Researchers are concerned that trucking colonies around the country to pollinate crops, where they intermingle with other bees from all over, helps spread viruses and mites among colonies. Additionally, such continuous movement and re-settlement is considered by some a strain and disruption for the entire hive, possibly rendering it less resistant to all sorts of systemic disorder.[69] One major US beekeeper reports moving his hives from Idaho to California in January, then to apple orchards in Washington in March, to North Dakota two months later, and then back to Idaho by November - a journey of several thousands of miles. Others move from Florida to New Hampshire or to Texas; nearly all visit California for the almond bloom in January. Keepers in Europe and Asia are generally far less mobile, with bee populations moving and mingling within a smaller geographic extent (although some keepers do move longer distances, it is much less common). This wider spread and intermingling in the US has resulted in far greater losses from Varroa mite infections in recent years.[70]
  37. 37. Bougainvillea (Nyctaginaceae) Bracts !
  38. 38. Poinsettia (Euphorbiaceae) Bracts !
  39. 39. Hummingbird, sunbird, and honeycreeper – nectar feeding bird pollinators
  40. 40. Pollination Syndromes • http://www.cas.vanderbilt.edu/bioimages/pa ges/pollination.htm
  41. 41. Unusually remarkable pollination stories • Thermogenic flowers and heat reward • Orchid with wasp pheromones and deception • Yucca moth and seed parasitism • Fig wasp and two female flower styles in syconium
  42. 42. Yucca – more tension/balance • http://waynesword.palomar.edu/ww0902a.htm
  43. 43. Figs! Reproductive captivity • Figs are one of many fruits that aren’t really fruits (also true of the strawberry, the apple and pear (!) the durian and several others…) • Fig wasps live and reproduce inside the “syconium” – a fig’s inflorescence • Ray’s Figs of Israel
  44. 44. Fig pollination • The puzzle of the fig • Wayne’s word on figs
  45. 45. Fertilization follows pollination • Pollination involves only the transfer of species-appropriate pollen to the receptive stigma of a flower • Fertilization requires the union of pollemn sperm nucleus with an ovule’s egg cell and creation of a new diploid (2n) embryo
  46. 46. Female sex cell is accompanied by accessory cells • Meiosis in the megasporangium of ovary (megasporocyte) creates eight (8) haploid cells – one of these eight is the egg cell, two nearby are called synergids. • Two other important nuclei are the polar bodies http://zygote.swarthmore.edu/plantfig8.gif
  47. 47. Male pollen must germinate and divide • Pollen grains on stigma actually germinate and grow a pollen tube to provide passage through style to ovary. http://www.msstate.edu/dept/biosciences/fishbein/pollentube.jpg http://www.cepceb.ucr.edu/images/members/lord/figure_1.jpg
  48. 48. Pollen tubes http://www.jmu.edu/biology/k12/fruitdev/fertil.htm
  49. 49. Pollen nucleus journey may be long! http://agbiosafety.unl.edu/education/lessons/breeding_lesson.htm Long corolla flowers like Chalice vine (Solandra) or trip from top silks of ear of corn to bottom kernels….
  50. 50. Pollen tube ultimately comprises 3 male nuclei • Tube nucleus is responsible for growth of pollen tube • Generative cell divides into two (2) (!) sperm nuclei by arrival at ovule entry (micropyle) http://zygote.swarthmore.edu/plantfig10.gif
  51. 51. Double fertilization • Following the division of the pollen’s sperm nucleus into two identical haploid nuclei, there are two separate fertilization events http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookflowersII.html http://www.hos.ufl.edu/amsweb/research.html
  52. 52. Double fertilization http://www.emunix.emich.edu/~ghannan/systbot/doublefertanimation.html
  53. 53. WHY have double fertilization? • Competing hypotheses • Review consequences of double fertilization • Shown at right, male and female gamete nuclei fusing to form embryo (top) and the 3 cells of 2nd fertilization fusing to form triploid cell to form endosperm(bottom) ♀ ♂ ♀ ♂
  54. 54. Pollen Viewer • http://www.geo.brown .edu/georesearch/esh/ QE/Research/VegDyn am/VegAnima/PV31I nst.htm

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