flowers
TRANSCRIPT
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)
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
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
Alternation of Generations
Why has the flower been such a success?
• Protection
• Pollination
• Dispersal
• Endosperm
• Evolutionary possibility – adaptive radiation
Protection
• Fruit helps prevent seed predation, resist dessication, may allow some seeds to last decades before germinating
Pollination
• Often deliberate, targeted, effective means of delivering gametes to target!
Dispersal
• Animal dispersed fruits, wind-dispersed seeds rely on evolved fruit forms – modifications of ovary not possible in non-flowering plants.
Endosperm
• Nutritive tissue derived from unique fertilization events – provides early energy reserves for embryo
Possibility
• Many specializations possible to modify original form
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
Calyx – The sepals
• Often green, but not always
• Frequently symmetric, in same number as petals
• Occasionally becomes a modified capsule that encloses fruit – tomatillo!
Corolla – The petals
• Note violet corolla of fused petals extending from a calyx of fused sepals in Datura!
Androecium – the stamens
• Anther held on extending filament
• May be attached to hypanthium or fused to petals
Androecium
Solandra maxima
K5 C5 A5 G2
Gynoecium – The carpels
• Fused style branches of multiple carpels may appear as a single central structure
http://www.csdl.tamu.edu/FLORA/imaxxgen.htm
Stamen and Stigma
Alstroemeria aurantiaca D. Don ex Sweet; photos Dan Zimmerman, FCSFlower courtesy of Dr. Melinda Yin
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
Actinomorphic and Zygomorphic•Actinomorphic
http://www.life.uiuc.edu/plantbio/260/Flowers/FloralTerms.html
zygomorphic
http://www.plantzafrica.com/plantnop/orchids/whatisorchid.htm
Jewelweed, Impatiens capensis Meerb.
Flower form - sympetaly
http://www.missouriplants.com/Redalt/Impatiens_capensis_page.html
Sympetaly = fused petals/tubular corolla
Zygomorphic Salvia patens Lamiaceae
Salvia flower, FCS Morris Arboretum Trip, October 13, 2007
Mints - Lamiaceae
http://www.eeob.iastate.edu/classes/botany306/terminology/flower/flowers.html
Hypogynous flower implies superior ovary
Perfect and Imperfect flowers
Begonia - imperfect
carpellate
staminate
http://www.botany.hawaii.edu/faculty/webb/BOT410/Angiosperm/FlowerCompletePerfect.htm
Perfect Hosta
Cucurbitaceae
• Imperfect flowers
Monoecious plant, staminate and carpellate
(imperfect) flowers
• Note the inferior ovary here
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
Many possible vehicles for pollination
• Wind• Insects (many
different groups!)• Birds• Bats • A few other mammals
Photographic database
Butterflies – vision & color
http://webexhibits.org/causesofcolor/17C.html
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
Nectar guides – visible or UV
Moth pollinators
• 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.
Isabel Friedman, Apis mellifera on Asteraceae, Morris Arboretum October 13, 2007
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)
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]
Bougainvillea (Nyctaginaceae)
Bracts !
Poinsettia (Euphorbiaceae)
Bracts !
Hummingbird, sunbird, and honeycreeper – nectar feeding bird pollinators
Pollination Syndromes
• http://www.cas.vanderbilt.edu/bioimages/pages/pollination.htm
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
Yucca – more tension/balance
• http://waynesword.palomar.edu/ww0902a.htm
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
Fig pollination
• The puzzle of the fig
• Wayne’s word on figs
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
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
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
Pollen tubes
http://www.jmu.edu/biology/k12/fruitdev/fertil.htm
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….
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
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
Double fertilization
http://www.emunix.emich.edu/~ghannan/systbot/doublefertanimation.html
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)
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Pollen Viewer
• http://www.geo.brown.edu/georesearch/esh/QE/Research/VegDynam/VegAnima/PV31Inst.htm