1. Faculty of Science, School of Sciences, Natabua Campus Lautoka
BIO706 Embryology Lectures: 16
Flower and Pollination - II

2. Floral variation and evolutionary trends
Earliest fossil flowers show:
many parts
parts spirally arranged rather than in whorls (rings)
parts separate, not fused to similar or different parts
ovary superior
radial symmetry.
Magnolia flower

3. Floral variation Some flowers have reduced numbers of parts
4’s and 5’s: Class Dicotyledonae (dicots)
3’s and multiples of 3: Class Monocotyledonae (monocots).
Magnolia flower

4. Floral variation Quiz: To which Class does each species belong?
Malva flower
Sagittaria flowers

5. Floral variation Parts may be fused
Example, petals fused to each other
Like parts fused: connation (ex., petals to petals)
Unlike parts fused: adnation (ex., stamens to petals)
Snapdragon flower

6. Floral variation
Fusing of petals can form floral tube (nectar made at bottom)
Only long-tongued pollinators can reach it.
Anisacanthus (Acanthaceae) flower

7. Floral variation Flowers with stamens and pistils: perfect flowers
Some flowers imperfect. Either pistillate (have pistil) or staminate (have stamens).
Pistillate flowers of Sagittaria
Staminate flowers of Sagittaria

8. Floral variation
Note: some species make pistillate flowers and carpellate flowers on separate individuals
This termed dioecious
Monoecious is when both sexes on same individual.

9. Floral variation Example of dioecious species: Persimmon (Diospyros)
Persimmon fruits
Example of dioecious species: Persimmon (Diospyros)
Pistillate
flower
Staminate
flower

10. Floral variation
Some flowers are missing one or more sets of basic parts: incomplete flowers
Note that all imperfect flowers are therefore incomplete!

11. Floral variation Floral symmetry:
Radial: can be divided into similar halves by several planes
Bilateral: can be divided into mirror images by 1 plane.

12. Floral variation Ovary position
Superior: other parts attach below ovary (hypogynous: “hypo-” =below, “gyn-” =female)

13. Floral variation
Example of superior ovary in a lily flower (ovary is E)

14. Floral variation Ovary position
Perigynous: ovary superior, but cup formed of fused sepals, petals, stamens around it.

15. Floral variation Ovary position
Inferior: other parts attach above ovary (epigynous: “epi-”=above, “gyn-”=female)

16. Floral variation
Example of inferior ovary: squash flower (this one is pistillate)
Ovary

17. Floral variation ray flowers disk flowers
Some flowers assembled into groups of flowers: inflorescence
Special inflorescence type: head
Example, sunflower and its relatives
Ray flowers have large fused petals (corollas fused), disk flowers small and crowded.
ray flowers
disk
flowers

18. Floral variation Flowering dogwood (Cornus florida)
Inflorescence, white structures are modified leaves (bracts) that act like petals.
Closeup showing individual
greenish flowers
Inflorescence

19. Pollination
Why flowers so varied? Many form mutualism with animals to achieve pollination
Most gymnosperms are wind pollinated
Must make lots of pollen in hope some reaches ovule in female (seed) cone. Most pollen falls to ground within 100 m of plant.

20. Pollination Some flowering plants are wind pollinated too
Ex, most grasses (corn, wheat, etc.), many temperate zone flowering trees (oaks, willows, maples, hickories)
Flowers usually small, no petals, no nectar, make lots of pollen.
Small, greenish
grass flowers

21. Pollination Most flowering plants are pollinated by animals
This usually viewed as mutualism (where both species benefit)
Plant gets pollen transferred
Animal gets “reward”
Pollen: high in protein
Nectar: sugary fluid produced by nectar glands (nectaries) in flower
Oils/Resins: some used as construction materials, “cologne” (male bee uses oil as female attractant).

22. Pollination
Benefits of animal pollination
1) Directed dispersal of pollen. Animal can take pollen directly to where plant wants it to go (stigma of flower of same species). Less waste of pollen

23. Pollination Benefits of animal pollination
2) Style of flower as “selective racetrack”
Keep in mind that 1 pollen grain can fertilize 1 ovule
Suppose 5 pollen grains arrive on stigma
Start to make pollen tubes
How many can fertilize an ovule?
2! First 2 to arrive!
Rest? LOSERS!
Pollen grains
stigma
style
ovary
2 ovules

24. Pollination Benefits of animal pollination stigma style ovary 2 ovules
2) Style of flower as “selective racetrack”
Pollen tubes are haploid (1n)
Haploid means only 1 allele (gene version) for every trait
If an allele is recessive, then it will be expressed (can’t be masked by another, dominant allele)
So, fittest (fastest) pollen grains mate
Inferior genes don’t get passed to offspring.
Pollen grains
stigma
style
ovary
2 ovules

25. Pollination Style of flower as “selective racetrack”
Is there evidence that this works?
Example, Coyote melon
Gourd growing in desert

26. Pollination Style of flower as “selective racetrack”
Study done in 2000 showed that
1) takes 900 pollen grains to fully pollinate flower
2) 1 pollinator visit puts 650 grains/flower. By 2 hours, >4000 grains deposited on stigma
3) Seeds produced from over-pollinated flowers produced more vigorous seedlings (compared to seeds from flowers with <900 pollen grains on stigma).

27. Pollination Style of flower as “selective racetrack”
Other studies with some crop plants have shown similar results.

28. Acknowledgement: Relevant book chapter and internet sources
Questions are welcome