Biology 2500: Botany

1
Lecture 19

• Biology 2500 Botany
• Chapter 22 Evolution of the Angiosperms

2
Learning Objectives

• Define
• Anthophytes
• Discuss
• Taxonomic significance of Magnoliids
• List
• Earliest angiosperm traits
• Recall
• When earliest angiosperms appeared
• Where (and when) angiosperms first achieved
  dominance
• Label
• Parts of a composite flower

3
The Anthophytes

• Collectively include
• 2 groups of gymnosperms
• Bennettitales
• Gnetophytes
• Angiosperms
• All share
• Pollen-borne sperm, which form a pollen tube

4
The First Angiosperms

• Earliest clearly angiosperm fossils from
  Cretaceous period, 130 mya
• Dominated N. hemisphere by 90 mya
• Also successful in S. hemisphere (see brown
  Gondwanaland below) by 80 mya

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Early Angiosperm Traits

• Possessed traits for drier environments
• Tough, desiccation-resistant leaves
• Vessel elements more efficient xylem
• Tougher seed coatresists embryo dehydration
• Also
• Sieve tubes for efficient phloem
• Better pollination, seed dispersal

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Magnoliids

• Along with the monocots and eudicots, this is a
  third group of angiosperms!
• Just 3 of the angiosperms
• At one time, were just grouped with eudicots as
  dicots
• More recent analysis says they deserve their own
  group
• Common Magnoliids
• Magnolias
• Tulip trees
• Have survived in warmer, humid climates, like mid
  Cretaceous period

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Early Perianth

• Sepals and petals about the same
• Some petals believed to be modified sepals
• Have same number of vascular strands as leaves
• Some petals believed to be modified stamens
• Only single vascular strand

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Early Stamens

• Were varied in structure
• Some, like modern magnolias, were colorful
• Some, green and fleshy
• Now, most are just filaments with an anther on
  top
• Nectaries are specialized sterile stamens, which
  provide nectar to attract pollinators

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7th Inning Stretch
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Insect Pollination

• Gave greater mobility to pollen
• Wind pollination is a lottery
• Insect pollination more precise, delivers much
  more pollen
• Competition between pollen became important!
• A race pollen tubes
• Competing to get onto pollinator very significant

11
General Trends in Flower Evolution

• Number of whorls (bunches of sepals, petals,
  stamens,) decreases over time
• Ovary becomes inferior more often than superior
• Radial symmetry early on, bilateral symmetry
  later on

12
Specialized Flowers

• The Asteraceae (of the eudicots) Orchidaceae
  (of the monocots) regarded to be most advance,
  specialized of flowers

13
Asteraceae

• The sunflowers, formerly Compositae
• Flowers are bunched into composite heads
• Disk flowers center portion of flower head
• Ray flowers outer portion of flower head
• Pappus modified sepals