Incomplete Flowers

Flower evolution

• Three types of floral modification are important in woody plants

  • fusion of parts

    

  • change in symmetry

  • floral reduction

    

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Flower symmetry

• Radially symmetrical flowers are called acitnomophic

• Bilaterally symmetrical flowers are called zygomorphic

Floral reduction

• Floral reduction can happen in a couple of ways:

  • flowers can become imperfect (male or female)

    • monoecious: both male and female on the same tree

    • dioecious: separate male and female trees

    • polygamodioecious: mostly dioecious, but some monecious

    • polygamomonecious: mostly monecious, but some dioecious

  • Floral reduction can happen in a couple of ways

    • flowers become imperfect

    • loss of petals and sometimes sepals (incomplete)

      • expose anthers and release pollen

      • increase pollen production (reallocation)

      • increase size of the stigma

      • wind-dispersed plants don’t need sepals or petals because trees that are wind pollinated don’t need colorful petals to attract insects

    • floral reduction can also combine both (e.g., staminate flowers with only sepals)

Flowers that are imperfect have: are lacking male or female parts

Floral reduction: Imperfect flowers

Pollination Biology and Ecology

• What might some evolutionary advantages for floral reduction?

  • reduce the likelihood of self-pollination

  • better for wind pollination

  • energy allocated toward more functional parts

• Pollination: the transfer of pollen from the anther to the stigma

  

Pollination and Fertilization of a Flower

• When does pollination become fertilization?

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• ovule: an immature (and unfertilized) seed

• seed: a mature (fertilized and developed) ovule

• Pollination Vectors (temperate zone, for trees)

  • Insects: in trees, developed first (most primitive)

    • Magnoliaceae, Ericaceae, Rosaceae

    • Flowers have petals for visibility

  • Wind: developed later, most trees are wind-pollinated

    • Fagaeceae, Betulaceae

  • Birds: mostly hummingbird

    • Aesculus, Albizia

• Insect pollination

  • flowers complete and perfect, or incomplete and imperfect

  • petals and sepals

  • large and sticky pollen

  • flowers at various times

  • nectaries present

  • shrubs and a few trees

• Wind pollination

  • flowers complete and imperfect

  • petals and sepals often absent

  • large amounts of small pollen

  • flowers before leaves emerge

  • no nectaries

  • almost all trees

  • seasonal allergies

• Cross-pollination: pollination between 2 or more trees

• Self-pollination (or selfing): pollination among flowers on the same tree

  • only 1% of loblolly pine has been found to be self-pollinated

• Imperfect flowers are always incomplete, but incomplete flowers may or may not be imperfect