Evolution of the Flower - Botany - Lecture Slides, Slides of Botany and Agronomy

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Evolution of the Flower

• Two classes - Monocotyledons and Dicotyledons
• Distinctive reproductive feature - carpels
• Angiosperms enclose their seeds in structures known as carpels, instead of lying naked on the scales of a strobilus as in gymnosperms. Hence the name "angiosperm" which means "seed in vessel".

• Cut into the pistil and you will see one or more tiny chambers, each chamber holding one or more sporangia on tiny stalks.
• These sporangia are the ovules - each carpel can hold one or several ovules
• Ovules in the ovary develop into seeds
• The ovary wall forms a fruit to help disperse the seeds
• There is an amazing diversity of floral structures. Linnaeus used these differences to classify plants.

• Pistils probably formed by the fusion of several

carpels along the midrib of the modified leaves.

• Goethe's "foliar theory of the carpel" is still the

best hypothesis for explaining the evolution of the

carpel.

Derived Features of

Angiosperms

• Leaves with finely divided venation
• Complex xylem - incl. vessels and parenchyma
• Complex phloem - sieve tube elements w/companion cells
• Herbaceous habit - rapid life cycle (some angios)
• Ovary to protect ovules ("seeds in vessels")
• Double fertilization and formation of triploid endosperm

Origin of the Angiosperms

Darwin called the origin of the angiosperms an "abominable mystery".

• The evolution of angiosperms remains a mystery to this day, although great progress has been made in recent years solving this mystery using a combination of fossil evidence, molecular data, and the discovery of the primitive angiosperm Amborella.
• Flowering plants evolved sometime during the Cretaceous , approximately 140 million years ago, while the dinosaurs were at their peak.

• However, no fossils showing a transition from gymnosperm to angiosperm have been discovered. This makes the origin of the angiosperms mysterious.
• Angiosperms quickly became the dominant plants, although gymnosperms continued to rule in cold, dry, or sandy habitats, as they still do today.
• Regardless of the origin of the angiosperms, by the end of the Cretaceous (65-70 mya) most flowering plant families had evolved.

• Flowers advertise their reward of nectar,

sugar water, to attract pollinators.

• Fruits function to disperse seeds.
  • Animals eat fruit, but don't digest seeds.
  • Tiny hooks and spines to attach to animal.
  • Also dispersed by wind, water (coconuts).

Monocots or Eudicots?

• Some flowering plants are neither monocots

or dicots.

• Magnolia

Parts of the flower provide clues

to evolution

• The perianth of early angiosperms did not have

distinct sepals and petals

• Sepals and petals were identical or there was a

gradual transition in appearance between these whorls (magnolias and water lilies).

• i.e. petals can be viewed as modified leaves that

have become specialized for attracting pollinators.

Wintergreen Chimphila umbellata Docsity.com

• Petal fusion resulting in a tubular corolla

figure 20-8c

The Stamens

• Magnoliids- broad, colored, and scented

role in attracting floral visitors

• In others- small greenish, fleshy
• Many living angiosperm in contrast have

thin filaments and thick terminal anthers

• In stamens of monocots and eudicots are

less diverse than Magnoliids