Flowers and Sex

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Flowers and Sex
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Flower parts are arranged into concentric rings
called whorls

• Sepals
• Petals
• Stamens
• Carpels

Arabidopsis flower from http//www.salk.edu/LABS/p
bio-w/gallery/ABC.jpg
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Berberidaceae Epimedium rubrum
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Cucurbitaceae Momordica charantia
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Brassicaceae Hesperis matrionalis
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Flower parts are arranged into concentric rings
called whorls

• Sepals
• Petals
• Stamens
• Carpels

Arabidopsis flower from http//www.salk.edu/LABS/p
bio-w/gallery/ABC.jpg
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When flower organ identity genes are lost in
Arabidopsis plants, specific whorls are missing
in mutant flowers
The organ identity mutants apetala1 (ap1) No
petals or sepals apetala2 (ap2) No petals,
unfused outer ring of carpels apetala3 (ap3) No
petals or stamens pistillata (pi) No petals or
stamens, many extra carpels agamous (ag) No
stamens or carpels, many extra petals
From Riechmann and Meyerowitz, Molec. Biol. Cell
1997, 8 1243.
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When all floral organ identity genes are lost,
all whorls give rise to leaves

• ag/ap2/ap3 triple mutant
• Is the leaf the base (default) state of a flower
  organ?
• Are all floral organs modified leaves?

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The perfect complete flower
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Vegetative organ whorls

• Sepals (collectively known as Calyx)
• Sometimes green or protective
• Outermost layer of flower
• Petals (collectively known as the Corolla)
• Sometimes large and colorful

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Female whorl

• A single pistil consists of a stigma, style and
  ovary
• female whorl gynoecium
• fusion of carpels
• The ovary produces ovule

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Male whorl

• Stamen typically consists of a filament and an
  anther (which contains pollen sacs)
• Most flowers have multiple stamen, known
  collectively as the androecium
• The anther pollen sac produces pollen- the male
  gametophyte

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Radial verses Bilateral symmetry
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Composite flowers are inflorescences composed
of many flowers

• Examples include thistle (b) wild dandelion (c)
  and sunflower (d)
• Disk flower
• Small fused petals called a corolla
• Ray flower
• Single enlarged petal, often brightly colored

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Flowers of Maize (Zea mays)
Tassle male flower
Ear female flower
Imperfect, incomplete flowers Tassles lack
carpels Ears lack stamens
Monecious Flower or flowers containing both sexes
are found in the same plant
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Perfect grass flower (example shown is Agropyron)
Catkin containing Incomplete flowers (male) from
Birch tree
Dioecious Organisms in which only one sex is
found in any individual (eg. Humans, Birch trees)
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Pollen

• Product of anthers (tops of stamen)
• Many shapes and sizes- each a signature for an
  individual species
• Palynology- the study of plants by examining
  pollen. Species identification, abundance,
  ecological range, climate studies
• Paleopalynology identification of fossil pollen.

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Wind pollenation

• Small dustlike pollen
• Smooth exterior
• High volume of pollen
• Small male flowers (i.e. grasses)
• Exposed stamen
• Feathery stigma (to pick up pollen from wind)
• Most often unisexual

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Insects as pollenators

• Bright showy petals
• Easy access to nectar and pollen
• Large sticky pollen
• Free food (nectar from nectaries at the base of
  the stamen and pollen)

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Birds as pollenators Kangaroo-paw

• Large flowers
• Convenient perch
• Overhead stamen and stigma touches the birds
  head
• Deep receptacle with large nectar production

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Aquilegia plant pollinated by a hummingbird
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Sexual mimicry

• Ophrys Orchid
• Mimics the shape and sent of a female bee
• As male bee attempts to copulate with orchid, it
  attaches 2 pollen sacs (yellow) to its head

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Key terms to know

• 4 floral whorls Sepals, petals, stamen, carpels
  and their components
• Perfection and Completeness of flowers
• Monoecious vs Dioecious organisms
• What 4 different pollination strategies?
• Why might you think that floral organs evolved
  from leaves?