Pollination systems
Pollination systems Pollination systems differ depending on how the flower opens and where and when the flower parts become receptive or shed pollen. 2. Cleistogamous The flower never opens and selfpollinates. 1. Chasmogamous The flower is open when shedding pollen. Bleeding heart Echinopsis 3. Hinged petals Flower is physically opened by the visiting insect. 4. Chambers Flower develops as a pollinator “trap”. Aristilochia Snap dragon (Antirrhinum) Back to main flower menu Next Back to main pollination menu Main menu Pollination systems Chasmogamous Chasmogamous flowers are open when they shed pollen. This pollen may fall on a receptive stigma in the same flower (self-pollinated) or be moved to a receptive stigma on a different flower (cross-pollinated). Chasmogamous flowers are common in Angiosperms. Lobelia Back to main flower menu Back Next Hibiscus Back to main pollination menu Main menu Pollination systems Chasmogamous Self-pollination is a sexual system where the flower is pollinated by pollen within the same flower. This type of system results in a high degree of pollination success, but low genetic variability in the seeds produced. Cross-pollination is where the flower is pollinated by pollen from a different flower usually from a separate plant. This type of pollination relies on a vector (wind, insect, bird, etc.) to move the pollen. The result are offspring with a higher degree of genetic variability. Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous Since self-pollination is an efficient pollination strategy that results in more uniform progeny. Many crop plants have been selected to be self-pollinated. Some species are highly self-pollinated (less than 4 percent cross-pollinated). Barley Crop plants that are highly selfpollinated include: Cereal grains sucha as barley (Hordeum), oats (Avena), wheat (Triticum), rice (Oryza). Legumes such as field pea (Pisum), and garden bean (Phaseolus). Back to main flower menu Back Next Bean Back to main pollination menu Main menu Pollination systems Chasmogamous There are also examples of crop plants that are self-fertile but can crosspollinate at more than 4 percent. These include crops like cotton (Gossypium), pepper (Capsicum), and tomato (Solanum). Tomato Pepper Cotton Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous In nature, many, if not most, species are naturally crosspollinated, a trait that seems to be desirable both for the individual and its population. Not only does the increased genetic diversity provide the opportunity for evolutionary adaptation within the population confronted with environmental change, but plant vigor also tends to be enhanced. Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous Morphological adaptations in flowers can facilitate cross-pollination. These include: Dioecy (dioecious flowers) Monoecy (monoecious flowers) Dichogamy Herkogamy Polymorphisms Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous - dioecious and monoecious Flowers may be bisexual having both male and female parts in the same flower (perfect flower) or unisexual with each flower being male or female only (imperfect flower). Bisexual Unisexual male Holly (Ilex) Cranesbill (Geranium) Back to main flower menu Unisexual female Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous - dioecious and monoecious One out-crossing strategy is for plants to produce male and female flowers that are physically separated. These unisexual flowers may appear on the same plant (monoecious) or be on separate plants (dioecious). Female flower Male flower Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous - dioecious Dioecious plants have pistillate (female) and staminate (male) flowers present in separate plants. Some noted dioecious plants include asparagus (Asparagus), pistachio (Pistacia) and holly (Ilex). Holly (Ilex) Aborted anthers Fertile anthers Stigma Female flower Back to main flower menu Back Next Male flower Back to main pollination menu Main menu Pollination systems Chasmogamous - monoecious Monoecious plants have pistillate (female) and staminate (male) flowers in separate flowers on the same plant. This system occurs in cucurbits (Cucurbita), corn (Zea), walnut (Juglans), oak (Fagus), chestnut (Castanea) and many conifers. Female flower Chestnut (Castanea) Back to main flower menu Back Next Male flowers Back to main pollination menu Main menu Pollination systems Chasmogamous – monoecious Banana (Musa) produces one large single inflorescence per stem and is monoecious with male and female flowers produces in separate rows of florets. Female flowers Male flowers Male flowers Back to main flower menu Back Next Female flowers Back to main pollination menu Main menu Pollination systems Chasmogamous – dichogamy Dichogamy is the separation of female and male flower function in time in bisexual flowers. In dichogamous flowers, pollen is shed before or after the stigma is receptive. Dichogamous flowers are referred to as having a male phase and a female phase of flowering. Dianthus This flower has stamens shedding pollen before the stigma is fully developed and receptive. Stamens Receptive stigmas Stigma The neighboring flower is older and has fully receptive female parts after the stamens have withered. Stamens Female phase Male phase Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous – dichogamy In an individual dichogamous flower, when the pollen sheds before the stigma is receptive it is called protandrous. When the stigma is receptive before the pollen sheds it is protogynous. The example below for pawpaw (Asimina) illustrates a protogynous flowering pattern. Stigma receptive before pollen is released. Receptive stigmas Stamens still developing Back to main flower menu Back Next Pollinated stigmas Pollen shedding after stigma has been pollinated by pollen from another flower. Stamens shedding pollen Back to main pollination menu Main menu Pollination systems Chasmogamous – dichogamy Balloon flower (Platycodon) is an example of a plant with protandrous flowers. Pollen shedding before the stigma is receptive. Stigma receptive after pollen is released. Stigma Stamens Stigma Back to main flower menu Stamens Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous – herkogomy Herkogamy is another method to facilitate out-crossing and reduce passive movement of pollen to the stigma in the same flower by physically separating the stigma and stamens. A common arrangement is to have the stamens below the elongated stigmas. Stigmas Stigmas Stamens Stamens Toad flower (Tricyrtis ) Back to main flower menu Magnolia Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous – herkogomy In glory lily (Gloriosa), the style makes a 90 degree turn to place the branched stigma away from the pollen shedding anthers. Stigma Stamens shedding pollen Style Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous – dichogamy and herkogomy Fireweed (Epilobium) combines both physical separation and dichogamy to ensure out-crossing. Stamens shedding pollen Fireweed relies on movement of the style to position the receptive stigma. When pollen is shedding from the stamens, the style is bent hanging the stigma below the flower. Once the flower has released all its pollen, the style raises up the now receptive stigma awaiting pollen from another flower. Back to main flower menu Back Next Non-receptive stigma Receptive stigma Back to main pollination menu Main menu Pollination systems Chasmogamous – polymorphisms Floral polymorphisms refer to different arrangements of flower parts in flowers from the same or different plants within the same species. Many of these adaptations are designed to alter the ratio of self- to cross-pollinated flowers. Long style; Short stamen filaments. Short style; Long stamen filaments. Tobacco (Nicotiana) Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous – polymorphisms Darwin described the different flower forms in primrose (Primula) referred to as being heterostylous. Plants exhibiting heterostyly have different flower morphologies where the style of the female and the filaments of the male are produced at different lengths. In primrose, the different flower forms are called pin and thrum. Primrose (Primula) Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous – polymorphisms In pin flowers, the long style extends the stigma in the corolla tube, while the anthers are held below the stigma on short filaments. In thrum flowers, the elongated filaments expose the anthers at the rim of the corolla tube and the style is shortened keeping the stigma below the anthers. This is a way to facilitate out-crossing as fertilization only occurs between pin and thrum flower forms. Pin Thrum Anthers Stigma Stigma Stigma Anthers Ovary Back to main flower menu Anthers Back Primrose (Primula) Next Ovary Back to main pollination menu Main menu Pollination systems Cleistogamous Cleistogamous flowers are not open when the pollen is shed from the anther. This leads to flowers that are self-pollinated. Cleistogamy is found in over 200 (mostly herbaceous) species. The reproductive effort invested in the cleistogamous flowers is smaller than in chasmogamous flowers. However, the potential genetic diversity in cleistogamous flowers can be less than the diversity from offspring from out-crossed chasmogamous flowers. Back to main flower menu Back Next Peanut (Arachis) is a crop plant with cleistogamous flowers. Back to main pollination menu Main menu Pollination systems Cleistogamous Bleeding hearts (Lamprocapnos spectabilis formerly Dicentra), has cleistogamous flowers. The outer two petals are pigmented and spurred. A pair of inner petals do not open and form a covering over the anthers and stigma. The enclosed stamens produce pollen that falls onto the enclosed stigma in the hanging flowers. Intact flower Floral parts separated Outer petal Pollen on the stigma Outer petal Stamens Stamens Stamens Stigma Back to main flower menu Back Inner petal Inner petals Lobelia Next Stigma Back to main pollination menu Main menu Pollination systems Chasmogamous and Cleistogamous Violets can produce both chasmogamous and cleistogamous flowers. This is a wonderful strategy because chasmogamy is designed for cross-pollination, while cleistogamy is designed for selfpollination. Chasmogamous flowers are produced in the spring or summer when pollinators are active and the flowers produce offspring (seeds) with generous genetic diversity. Back to main flower menu Back Next Chasmogamous flowers in sweet violet (Viola odorata). Back to main pollination menu Main menu Pollination systems Chasmogamous and Cleistogamous Cleistogamous violet flowers are produced at and under the soil surface and do not require pollinators. Although this restricts genetic diversity, it provides insurance against poor seed production from earlier out-crossing chasmogamous flowers. Fruits Fruit Back Fruits Soil removed around violet plant’s crown. Leaf litter removed. Back to main flower menu Flower Next Back to main pollination menu Main menu Pollination systems Chasmogamous and Cleistogamous Subterannean cleistogamous flowers in sweet violet (Viola odorata) are produced in the summer through early autumn. Subterranean cleistogamous flower and fruit Fruits Flower Flower Fruit Flowers never opens Fruit Back to main flower menu Back Next Seeds Back to main pollination menu Main menu Pollination systems Chasmogamous and Cleistogamous Wood sorrel is another species that produces both chasmogamous and cleistogamous flowers. Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Chasmogamous and Cleistogamous Beechdrops (Epifagus americana) is a root-attached, parasitic plant specific to beech (Fagus) tree roots. Beechdrops produces open (chasmogamous) cross-pollinating flowers at the top of the inflorescence and closed (cleistogamous) selfpollinating flowers at the base of the inflorescence. Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Hinged petals In flowers with hinged petals, the flower must be physically opened by a visiting insect. This restricts access to pollinators with the strength and dexterity to open the flower like bees. Physically opening a snapdragon flower Snapdragon (Anthurinum) Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Hinged petals Bees must force their way under the keel flower petal in wild pea to reach their pollination reward and subsequently move pollen from flower to flower. Wild pea (Centrosema) Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Hinged petals Other flowers with hinged petals include golden corydalis and turtlehead. Golden corydalis (Corydalis aurea) Back to main flower menu Back Next Turtlehead (Chelone glabra) Back to main pollination menu Main menu Pollination systems Floral traps Floral traps are highly modified flowers that usually entice pollinators by a strong, fetid odor. “Traps” enclose the insect to facilitate pollination. Insects may be trapped for a brief time (1 to 5 days), or in some cases never released from the trap. Rosary vine (Ceropegia ) is generally fly pollinated and traps visitors for approximately 24 hours. Back to main flower menu Back Next Back to main pollination menu Main menu Pollination systems Floral traps Floral traps have evolved in at least eight families and are well represented in the Aristolochiaceae and Araceae. Trap flower mechanisms are described in detail in the mimicry and deceit section under pollination. Arisaema Caladium Back to main flower menu Back Aristolochia Back to main pollination menu Main menu
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