Presentation on theme: "Flowers Extraordinary diversity of color, size, form Universal in objective – sexual reproduction for a rooted, stationary land plant! 88% of all known."— Presentation 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:
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
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 K 5 C 5 A 5 G 2
Gynoecium – The carpels Fused style branches of multiple carpels may appear as a single central structure
Stamen and Stigma Alstroemeria aurantiaca D. Don ex Sweet; photos Dan Zimmerman, FCS Flower courtesy of Dr. Melinda Yin
Floral Formula - KCAG K (or CA) Calyx C (or CO) Corolla A Androecium G Gynoecium
Actinomorphic and Zygomorphic Actinomorphic zygomorphic
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)
Many possible vehicles for pollination Wind Insects (many different groups!) Birds Bats A few other mammals Photographic database
Butterflies – vision & color
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.
Nectar guides – visible or UV
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. 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.
Bougainvillea (Nyctaginaceae) Bracts !
Poinsettia (Euphorbiaceae) Bracts !
Hummingbird, sunbird, and honeycreeper – nectar feeding bird pollinators
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
Figs! Reproductive captivity Figs are one of many fruits that arent 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 figs inflorescence Rays Figs of Israel
Fig pollination The puzzle of the fig Waynes 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 ovules 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
Male pollen must germinate and divide Pollen grains on stigma actually germinate and grow a pollen tube to provide passage through style to ovary.
Pollen nucleus journey may be long! 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)
Double fertilization Following the division of the pollens sperm nucleus into two identical haploid nuclei, there are two separate fertilization events
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 2 nd fertilization fusing to form triploid cell to form endosperm(bottom)