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