Chapter 20 Evolution of Angiosperms

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Chapter 20Evolution of Angiosperms
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Angiosperms

• Gymnosperms mostly wind pollinated
• Angiosperms mostly insect/animal pollinated
• insect pollination thought to drive early angio.
  evolution
• Unique characteristics of angiosperms suggest
  single ancestor
• monophyletic
• flowers, closed carpels,
  double
  fertilization, endosperm,
  3-nucleate
  microgametophyte,
  8-nucleate
  megagametophyte,
  2 pollen sacs per stamen,
  
  seive tubes and companions cells
• Angiosperms 1st appear 130 MYA
• eventually dominant vegetation

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Basic Evolution

• Magnoliids are primitive ancestors of monocots,
  eudicots
• neither monocot or eudicot
• pollen w/ single aperature
• ethereal oils (nutmeg/pepper/laurel)
• woody magnoliids
• Magnoliaceae
• Lauraceae
• Calycanthaceae
• rise to eudicots
• paleoherbs
• Piperaceae
  Aristolochiaceae
  
  Nymphaeaceae
• rise to monocots

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Basic Evolution

• Adaptive features for drought and cold
• tough/small lvs, vessel elements, resistant seed
  coat
• deciduous habit allows dormancy during
  drought/excessive heat or cold
• sieve-tube elements (P) and
  vessel elements (X)
  allow
  more rapid transport
• specialized pollination and
  seed dispersal
  mechanisms
• chemical diversity for defense
  systems

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Evolution of the Flower

• Perianth of early angiosperms
• calyx and corolla similar looking
• petals derived from sepals
• modified lvs for attraction
• 1 vascular strands
• petals also derived sterile stamens (b/c 1
  vascular strand)
• petals fuse to make tubular corolla

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Evolution of the Flower

• Stamens of early angiosperms
• diversity of color/scent/size/thickness/anther
  location
• colored/scented to attract pollinators
• thick filaments
• may have fused stamens/filaments forming columns
• nectaries sterile stamens
• secrete nectar
• bait for pollinators
• Carpels of early angiosperms
• leaflike carpels w/o specialization
  for trapping
  pollen
• free vs fused (modern) carpels
• incomplete closure vs closed (modern) carpels

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Evolution of the Flower

• 4 trends in and arrangement of floral parts
• ? variability and indefinite of parts ?
• ? parts that are definite in
• 4 whorls of flower parts on longer axis ?
• 1, 2, 3 or 4 whorls, often fused on short
  axis
• superior ovary, distinct calyx and corolla ?
• inferior ovary, similar calyx and corolla
• radial symmetry (regular, actinomorphic) ?
• bilateral symmetry (irregular, zygomorphic)

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Asteraceae (Compositae)

• Eudicot, 22,000 sp., widely dispersed
• Flower arrangement
• tiny, epigynous flowers clustered in head
• inferior ovary
• 1 ovule and locule w/ 2 fused carples
• 5 fused stamens, 5 fused petals
• sepals reduced to scales/bristles/barbs
  (pappus)
• aid dispersal
• 2 flower types
• disk flowers in center, actinomorphic
• ray flowers around edge, carpellate or
  sterile, fused corollas,
  zygomorphic
• mature in spiral pattern

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Orchidaceae

• Monocot, 24,000 sp.,
  mostly tropical
• Flower arrangement
• 3 fused carpels, inferior ovary w/ 1000s ovules
• 1 stamen fused to style and stigma
  (fused structure
  column)
• anther contents held together
  (pollinium)
• 3 petals (2 wing-like, 1 showy lip),
  3 sepals (petal-like)
• zygomorphic
• Some mycoheterotrophic

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Coevolution of Flowers and Insects

• Coevolution process when 2 sp. act as
  selective forces on each other
• Attractiveness to insects ? visitation ? seed
  production
• Phenotypic changes resulting in ? visitation
  
  reproductive advantage
• edible flower parts
• nectaries, pollen
• color, shape, scents
• Pollination trend
• water ? wind ? animal
• reward pollen and nectar
• more efficient

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Coevolution of Flowers and Insects

• Protected/covered ovules (inferior ovary) ?
  protection from animal browsing
• Bisexual flowers ? efficient pollination
• Insect pollination ? angiosperm and insect
  diversity
• specializations catering
  to specific
  pollinators

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Beetle Pollination

• Beetle pollinated flowers white/dull color,
  strong odors (fruity/spicy/foulness)
• Rewards nectar/pollen/edible fleshy plant parts
• Inferior ovaries offer
  protection

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Bee Pollination

• 20,000 sp. of bees
• Bees pollinate most sp.
• ? eat nectar, ? eat nectar/pollen
• Specialization for carrying nectar/pollen
  mouthparts/ body hairs/appendages
• See UV light, not red
• Bee pollinated flowers
  blue or yellow color,
  
  special markings,
  landing platforms

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Moth and Butterfly Pollination

• Diurnal moth/butterfly pollinated flowers
  long/slender/ tubular flowers or spur b/c
  long/coiled tongues
• similar to bee pollinated flowers
  (sweet/colorful)
• see red thus orange/red
• Nocturnal moths white/pale color, strong/sweet
  smell after sunset

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Bird Pollination

• Bird pollinated flowers ? nectar, often
  large/clustered, often red/yellow, odorless
• Typically sp. specific
• Hummingbirds impt pollinator
• Apparatus to exclude non-pollinating sp.
• upside down flowers
• long tubes
• red, odorless

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Bat Pollination

• Bat pollinated flowers large, lots of nectar,
  dull color, strong odor, open at night, tubular,
  hang beneath lvs
• ¼ bats are herbivores
• ? protein levels
• 130 genera pollinated by bats
  
• bananas, mango, sisal
• Bat adaptations
• slender/long muzzles
• long tongues
• small front teeth

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Wind Pollination

• Wind pollinated flowers no nectar, dull color,
  odorless, reduced petals
• Mostly temperate sp. w/ ? population density
• Occurs before lvs come out
• Inefficient
• Means of ensuring outcrossing
• dioecious or monoecious
• self-incompatibility
• Adaptations for wind pollination
• suspended anthers
• smooth pollen
• large feathery stigmas
• inflorescences w/ many flowers

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Aquatic Plants

• 380 genera submerged, aquatic plants
• Most insect or wind pollinated
• Underwater pollination threadlike pollen grain

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Pigments

• Color impt pollinator attractor
• Pigment ? in flower parts
• Flavonoids provide UV protection
• anthocyanins red, blue
• stored in vacuoles
• color depends on pH
  
• red acid, blue alkaline, violet neutral
• flavonols colorless, white, ivory
• Carotenoids red, orange,
  yellow
• stored in plastids
• Betacyanins reddish

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Evolution of Fruits

• Megs Talk

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Biochemical Evolution

• 2 metabolites (alkaloids, quinones,
  essential oils, glycosides,
  flavonoids,
  raphides)
• ? palatability
• antiherbivory
• Brassicaceae (mustard, cabbage, brocolli)
• glycosides
• ? specialized herbivores accumulate
  
• deter predators
• Asclepias (milkweed, butterflyweed)
• alkaloids and cardiac glycosides
• induce gastric distress, vomiting, heart failure
• monarch butterfly, viceroy butterfly

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Biochemical Evolution

• Cannabis sativa (marijuana)
• THC
• Papaver somniferum (opium poppy)
• opium
• Toxicodendron radicans (poison ivy)
• 3-pentadecanedienyl
• Lophophora (peyote cactus)
• mescaline
• Solanum (wild yams)
• 16D, contraceptives