1. School of Sciences, Lautoka Campus BIO509 Botany Lecture 18: Angiosperms
Photo courtesy of Prof. Randy Thaman

2. Angiosperms Commonly known as “flowering plants”.
Produce the reproductive structures called flowers & fruits.
Extremely diverse: approximately 250,000 known species (compared to 720 gymnosperm spp.)
90% of land plant
species.

3. Angiosperms originated approximately 140 mya.
Occur in a single phylum – Phylum Magnoliophyta (previously known as the Anthophyta.
By comparing the genes that give rise to flowers & cones, scientists hypothesize that flowers evolved from the pollen-producing reproductive structures of a gymnosperm ancestor.

4. Change from a gymnosperm and fern
dominated world to a world
dominated by fast-growing
angiosperms was one of the most
important changes in the history
of earth.

5. Which group of gymnosperms is most closely related to angiosperms?

6. Learning outcomes
Know the similarities and difference between angiosperms and gymnosperms.
Understand the major trends of specializations in flowering plants
Know the reproductive structures and lifecycle of a flowering plant.
Know the characteristics of flowers associated with specific types of pollinators.

7. Angiosperms
Are flowering plants that form seeds inside a protective chamber called an ovary.
  Greek words
“angeion” – vessel “ sperma” – seed
“Vessel” is the carpel which is like an inrolled leaf with seeds along its margin.
Primitive flowers had ovules on the edge of the leaf-like sporophyll. Through evolution, the edges of the carpel gradually rolled in and fused to enclose the ovules.

9. General characteristics of angiosperms
The flower is the defining reproductive adaptation of angiosperms.
                       
Flowers are made up of four types of modified leaves- sepals, petals, stamens, and carpels.
                                   
Stamens are the male reproductive organs that produce microspores.
Carpels are female reproductive organs that produce megaspores.

10. General characteristics of angiosperms
Angiosperms (except Amborella which is a primitive flowering plant) have xylem with both tracheids and vessel elements for conduction, as well as fiber cells for support.
In gymnosperms, the only cell type found in xylem tissue is tracheids.

11. Review of Flower Structure
Sepals (infertile) – enclose & protect the floral bud.
Petals (infertile) – attract pollinators.
Stamen (fertile) – made of a filament (stalk) & anther (site of pollen production).
Carpel (fertile) – consists of a stigma (pollen landing site), style, & ovary (location of ovules).
All floral organs attached to the stem at the receptacle.

12. How does this differ from the reproductive structures of the gymnosperms?

13. Floral Variations Complete vs Incomplete flowers
all 4 basic floral organs present = complete flower
1 or more floral organs absent = incomplete flower
- Flowers can be sterile, female (carpellate), male (staminate)
- Creates monoecious & dioecious plants
Complete flower
incomplete flower

14. Hibiscus is a complete flower (has all 4 basic floral organs)

15. Grass flower is incomplete (lacks petals)
Why might petals be unimportant for grasses?

16. Floral Variations
Bilateral vs. radial symmetry

17. Floral Variations
Superior, semi-inferior, or inferior ovary position

18. Floral Variations Individual or clustered flower distribution.
- clusters are called inflorescences
other: size, shape, color, odor, arrangement of floral organs

19. Reproduction in angiosperms
Are heterosporous like the gymnosperms.
Sporophytes are the most dominant.
Female gametophyte is wholly enclosed within the sporophyte tissue and reduced to only a few cells.
Male gametophyte consist of a pollen grain with three nuclei.

20. Male Gametophyte = Pollen Grain
Develop within microsporangia located in anthers.
Diploid cells within microsporangia divide by meiosis to produce microspores.

21. Microspores develop into pollen grains
Pollen grains become mature gametophytes when the generative nucleus divides & forms 2 sperm (usually occurs post-pollination)

22. Female Gametophyte = Embryo Sac
Develop within megasporangia located within ovules.
Each megasporangium contains 1 large diploid cell that divides by meiosis to produce 4 haploid cells but only one survives (megaspore).

23. The megaspore divides 3 times by mitosis producing a large cell with 8 haploid nuclei (four at each end).
One from each migrates to the centre and forms the polar nuclei.
Antipodal and synergid cell have no apparent function and degenerate.
One cell functions as the egg (closest to microphyll)

24. Pollination Transfer of pollen from an anther to a stigma.
When successful, pollen grain produces a pollen tube which grows through the style to the ovary where it releases two sperm into the embryo sac.

25. Pollination is brought about by insects, wind,
water, birds, bats, and other mammals.
Flowers are specially adapted to attract and
accommodate the pollinating agents.

26. Questions??