1. Seed Plants: Angiosperms
Chapter 23

2. Outline Introduction Phylum Magnoliophyta – The Flowering Plants
Development of Gametophytes
Pollination
Fertilization and Development of the Seed
Apomixis and Parthenocarpy
Trends of Specialization and Classification in Flowering Plants
Pollination Ecology

3. Introduction Angiosperms = flowering plants
Seeds enclosed in carpel – resembles folded over leaf and fused at margins
Pistil composed of single carpel, or >2 united carpels
Bleeding hearts
Seed develops from ovule within carpel
Ovary becomes fruit

4. Introduction Angiosperms = Phylum Magnoliophyta
Divided into 2 large classes:
Magnoliopsida - Dicots
DNA and cladistic evidence suggest 2 groups of dicots should be recognized
Liliopsida - Monocots
Flower = modified stem bearing modified leaves
Most primitive flower
Long receptacle
Many spirally arranged flower parts that are separate and not differentiated into sepals and petals (= tepals)
Flattened and numerous stamens and carpels

5. Phylum Magnoliophyta – The Flowering Plants
Heterosporous
Sporophytes dominant
Female gametophytes wholly enclosed within sporophyte tissue and reduced to only few cells
Male gametophytes consist of germinated pollen grain with 3 nuclei

6. Phylum Magnoliophyta Development of gametophytes - Female:
2n megasporocyte differentiates in ovule
Undergoes meiosis and produces 4 1n megaspores
3 degenerate
Remaining cell enlarges and nucleus divides to produce 8 nuclei (without walls)
Outer 2 layers of ovule differentiate into integuments that later become seed coat
Micropyle at one end of ovule

7. Phylum Magnoliophyta Development of gametophytes – Female cont’d.:
8 nuclei form 2 groups, 4 near each end of cell
1 nucleus from each group migrates to cell middle and form central cell
Cell walls form around remaining 6 nuclei
Egg and 2 synergids closest to micropyle
3 antipodals at opposite end
Female gametophyte = megagametophyte or embryo sac

8. Anther with microspores
Phylum Magnoliophyta
Development of gametophytes - Male:
Formation of male gametophytes takes place in anthers
4 patches, corresponding to pollen sacs, of microsporocyte cells differentiate in anther
Each microsporocyte undergoes meiosis to produce 4 1n microspores
Anther with microspores

9. Phylum Magnoliophyta Development of gametophytes – Male cont’d.:
Microspores undergo 3 changes:
Divide once by mitosis to form small generative cell inside larger tube cell
Nucleus of tube cell = vegetative nucleus
Members of each quartet of microspores separate
Wall becomes 2-layered
Outer layer (= exine) finely sculptured and contains chemicals that react with chemicals in stigma
Generative nucleus divide to produce 2 sperm
Pollen grain

10. Phylum Magnoliophyta Pollination:
Pollination - transfer of pollen grains from anther to stigma
Self-pollination - pollen grains germinate on stigma of same flower
Fertilization - union of sperm and egg
Pollination by insects, wind, water, animals or gravity

11. Phylum Magnoliophyta Fertilization and development of the seed:
After pollination, further development of male gametophyte may not take place unless pollen grain:
From different plant of same species
From variety different from that of receiving flower
Pollen tube grows between cells of stigma and style until reaches ovule micropyle
Vegetative nucleus stays at tips of pollen tube, while generative cell lags behind and divides into 2 sperm
Pollen tube enters female gametophyte, destroying synergid in process, and discharges sperms

12. Phylum Magnoliophyta
Fertilization and development of the seed cont’d.:
Mature male gametophyte = germinated pollen grain with vegetative nucleus and 2 sperms within tube cell

13. Phylum Magnoliophyta
Fertilization and development of the seed cont’d.:
Double fertilization:
1 sperm unites with egg, forming zygote, then embryo
Other sperm unites with central cell nuclei, producing 3n endosperm nucleus developing into endosperm tissue
Endosperm tissue = nutritive tissue for embryo

14. Phylum Magnoliophyta
Fertilization and development of the seed cont’d.:
Endosperm becomes extensive part of seed in some monocots (i.e., corn and other grasses)
Endosperm absorbed into cotyledons in most dicots
Ovule becomes seed, ovary matures into fruit, integuments harden into seed coat

15. Phylum Magnoliophyta
Fertilization and development of the seed cont’d.:
Other types of (female) gametophyte development:
Female gametophyte can have from 4 to 16 nuclei or cells at maturity
Endosperm may be 5x, 9x or 15x

16. Phylum Magnoliophyta Apomixis and parthenocarpy:
Apomixis - without fusion of gametes but with normal structures otherwise being involved
Embryo from 2n nutritive cell or other 2n cell of ovule, instead of from zygote
Results in vegetatively propagated plant
Parthenocarpy - fruits develop from ovaries with unfertilized eggs.
Results in seedless fruits
Navel oranges and bananas

17. Phylum Magnoliophyta
Trends of specialization and classification in flowering plants:
1st historical classifications for convenience
Modern botanists group plants according to natural relationships based on evolution
Fossil record suggests flowering plants 1st appeared about 160 mya during late Jurassic
Flowering plants developed during Cretaceous and Cenozoic
Dominant plants today

18. Phylum Magnoliophyta
Trends of specialization and classification in flowering plants cont’d.:
1st pistil from leaflike structure with ovules along margins = carpel
Edges of blade rolled inward and fused together
Separate carpels of primitive flowers fused together to form compound pistil consisting of several carpels

19. Phylum Magnoliophyta
Trends of specialization and classification in flowering plants cont’d.:
Inferior ovary (epigynous flower) - receptacle or other flower parts fused to ovary and grown up around it
Superior ovary (hypogynous flower) - ovary produced on top of receptacle
Perigynous flowers - flower parts attached to corolla tube of fused petals, creating floral tube not attached to ovary

20. Female flower with inferior ovary
Phylum Magnoliophyta
Trends of specialization and classification in flowering plants cont’d.:
Male flower
Female flower with inferior ovary
Complete flower - has calyx, corolla, stamens and pistil
Incomplete flower - corolla or other flower parts missing
Perfect flower - both stamens and pistil present

21. Female flower with inferior ovary
Phylum Magnoliophyta
Trends of specialization and classification in flowering plants cont’d.:
Male flower
Female flower with inferior ovary
Imperfect flower - either stamens or pistil missing
Monoecious species - male and female imperfect flowers on same plant
Dioecious species - plant bears only male flowers and other plants bear only female flowers

22. Phylum Magnoliophyta
Trends of specialization and classification in flowering plants cont’d.:
Primitive flowering plants
Simple leaves
Flower with numerous, spirally arranged parts, not fused to each other
Flowers radially symmetrical = regular.
Flowers complete and perfect
Superior ovary (hypogynous flower)
Magnolia

23. Phylum Magnoliophyta
Trends of specialization and classification in flowering plants cont’d.:
Specialized flowering plants:
Flower parts fewer and definite in #
Spiral arrangements compressed to whorls
Bilaterally symmetrical flowers = irregular
Orchid

24. Phylum Magnoliophyta
Trends of specialization and classification in flowering plants cont’d.:
Specialized flowering plants cont’d.:
Reduction and fusion of parts
Incomplete or imperfect flowers
Inferior ovary
Orchid

25. Pollination Ecology Pollinators co-evolved with plants
20,000 bee species among current-day pollinators
Bee-pollinated flowers:
Generally brightly colored, mostly blue or yellow
Often have lines or distinctive markings, may function as guides to lead bees to nectar
Bees see UV light (humans do not)
In ordinary light
In UV light

26. Pollination Ecology Beetle-pollinated flowers:
Strong, yeasty, spicy or fruity odor
White or dull in color
Some do not secrete nectar, but furnish pollen or food on petals in special storage cells
Fly-pollinated flowers:
Smell like rotten meat
Dull red or brown

27. Pollination Ecology Butterfly- and moth-pollinated flowers:
Often have sweet fragrances
White or yellow for night-flying moths
Sometimes red, often blue, yellow or orange for butterflies
Nectaries at bases of corolla tubes or spurs for long tongues

28. Pollination Ecology
Bird-pollinated flowers (hummingbirds and sunbirds):
Often bright red or yellow
Little if any odor - Birds don’t have keen sense of smell
Large and part of sturdy inflorescence
Copious amounts of nectar - Birds highly active
Long floral tubes

29. Pollination Ecology Bat-pollinated flowers: Primarily in tropics
Open at night when bats foraging
Dull in color
Large enough for bat to insert head or consist of ball-like inflorescence containing large numbers of small flowers

30. Pollination Ecology Orchid flowers:
Have pollinators among all types mentioned
Some adaptations between orchid flowers and pollinators extraordinary.
Pollen grains produced in little sacs called pollinia (singular: pollinium) with sticky pads at base
Ophrys

31. Review Introduction Phylum Magnoliophyta – The Flowering Plants
Development of Gametophytes
Pollination
Fertilization and Development of the Seed
Apomixis and Parthenocarpy
Trends of Specialization and Classification in Flowering Plants
Pollination Ecology