1. FLOWERS Notes for Biology 2410* at Utah State University
*Plants and fungi: ecosystem essentials

2. Flowers: A Marvelous Innovation
Flowering plants first appeared around 140 million years ago (Upper Jurassic).
Oldest flower fossil is 125 million years old.
The dominant forms of plant life were gymnosperms, cycads, and ferns.

3. Today
Flowering plants are now the dominant form of plant life over most of the earth’s land surface.
Ferns are rarely dominant and gymnosperms are dominant only in cold, or seasonally cold locations. Cycads are hanging on by a thread.
Why have flowering plants been so successful?

4. Flowers Double fertilization: saves energy
Ovaries protect ovules and developing seeds; mature into fruits that promote seed dispersal
Floral structure encourages pollinator fidelity; nectar and pollen to reward pollinators
Fast reproductive cycle compared to gymnosperms
Shorter haploid phase (a genetically risky phase) than all other plants

5. Origin of benefits Some benefits derive from structure of flower
Some benefits derive from short reproductive cycle
Some benefits from double fertilization
Many benefits derive from evolutionary modifications within the flowering plant lineage

6. Structure of flowers
Flowers are composed of four whorls. From the outside in, they are:
Calyx (sepals)
Corolla (petals)
Androecium (stamens)
Gynoecium (pistils)

7. Calyx Outermost whorl Usually green Protects developing flower
Physically
Chemically
Made up of SEPALS
Sepals free or not
Calyx radially or bilaterally symmetric

8. Corolla Is usually colorful and showy; Attracts pollinators
Guides pollinators;
Is composed of petals
Petals may be united or separate;
Corolla may be radially or bilaterally symmetric.

9. Androecium Is composed of stamens Stamens have filaments and anthers
Pollen is produced in anthers
Stamens can be free or united

10. Gynoecium Is composed of pistils
A pistil is composed of an ovary, style, and stigma.
Styles may be separate, branched, or united
Pistils have a slide of their own – just wait

11. Hypanthium
If the corolla and calyx are attached to a cup or tube that is then attached to the receptacle, the cup or tube is called a hypanthium.
If a hypanthium is present, the perianth may be
hypogynous
perigynous
epigynous

12. Flower structure (2)
Perianth refers to the combination of the calyx and corolla.
Used
when the two are very similar (tulips)
to refer to both structures at the same time

13. Receptacle
The top floral whorls are attached to the receptacle – the tissue where the stalk to the flower changes to being part of the flower

14. Pedicels Flowers are borne on pedicels
Think of a pedicel as the stalk to a flower

15. Pistils
Composed of
Stigma – landing platform for the pollen grains, first selection point
Style – helps select among pollen tubes; may be branched
Ovary – contains ovules; matures into fruit

16. Ovaries (and fruits) Ovaries protect the ovules and developing seed
Become fruits, modified for seed dispersal.
Fruits may have other parts of flower attached.

17. Identifying Flowering Plants
To survive, species must reproduce
Pollination is the first major step in the reproduction of seed plants like gymnosperms and flowering plants
Flowers persuade animals to serve as pollinators, preferably faithful pollinators
To get the right pollen, flowers need to be memorable so …

18. Start thinking like a pollinator
Is there a reward?
How can I find another like this one?
Symmetry – radial or bilateral
Color pattern
Odor
Will it be safe for me?
Corolla – united or separate petals
Corolla more important than calyx – why?
Can I reach the reward and is it adequate?
nectaries and androecium

19. Next, start counting … sepals (or calyx lobes)
petals (or corolla lobes)
stamens
pistils
style branches
Ovary and 2-branched style

20. Then look at the ovary position
Above the calyx and corolla (ovary superior; perianth hypogynous)
Below the calyx and corolla (ovary inferior; perianth epigynous)
One more possibility exists …

21. And that possibility is …
Ovary partially inferior
Ovary partially inferior; perianth perigynous
Perianth
perigynous

22. And finally, the glories of the gynoecium …
How many pistils are there?
How many styles or style branches?
How many chambers are there in the ovary (need a cross-section)
Where are the seeds attached?

23. Still part of the ‘little more’
Each theoretical leaf unit is termed a carpel
A pea pod is a mature pistil made up of 1 carpel
Pistils with 2 style branches and/or chambers in the ovary are said to have 2 carpels
Pistils with 3 style branches and/or chambers are said to have 3 carpels etc. etc.

24. And that is enough to start …
Assignment:
Pick 4 non-cultivated plants and carefully examine their flowers. Show you understand its structure by completing the handouts.

25. Why a non-cultivated plant?
Many cultivated plants have been selected for their abnormalities, which often makes it difficult for beginners (and even old-timers) to identify them.
Most identification keys include a very few purely cultivated plants so the chances are good that a cultivated plant is not in the key.