Overview
This lecture reviews the basic components of a flower, key terminology, and introduces evolutionary variations and pollinator relationships. Flower structure, classification, and the concept of flower formulas are discussed for plant identification.
Basic Flower Structure
- A complete flower has four whorls: sepals (outer), petals (inner), stamens (male), and carpels (female).
- Sepals protect the developing bud; petals attract pollinators.
- Stamens contain anthers (produce pollen with two sperm) and filaments.
- Carpels include stigma (pollen landing site), style, and ovary (contains ovules).
Flower Types & Variation
- Dicots have flower parts in fours or fives; monocots in threes.
- A perfect flower has both stamens and carpels; an imperfect flower has only one.
- Complete flowers have all four whorls; incomplete flowers lack one or more.
- Monoecious plants have separate male and female flowers on the same plant.
- Dioecious plants have male and female flowers on different plants.
Pollination & Evolution
- Pollination: transfer of pollen from anther (male) to stigma (female).
- Co-evolution: flowers and pollinators influence each other's evolution via selective pressure.
- Genetic diversity is increased by self-incompatibility (e.g., cherries).
- Human intervention (cross-pollination) is common in ornamental plants like hibiscus.
Ovary Position & Flower Classification
- Superior ovary (hypogynous): ovary sits above other flower parts.
- Inferior ovary (epigynous): ovary is below other flower parts.
- Perigynous: flower parts attached partway up the ovary.
Flower Formula
- Flower formula summarizes structure: symmetry (radial or bilateral), number of sepals, petals, stamens, and carpels, and fusion of parts.
- Radial symmetry = regular; bilateral = irregular.
- Fusion within or between whorls is noted in the formula.
Key Terms & Definitions
- Whorl — a ring of similar plant structures (sepals, petals) arranged around a flower.
- Stamen — male reproductive part; includes filament and anther.
- Carpel (Gynoecium) — female reproductive part; includes stigma, style, ovary.
- Perfect Flower — has both stamens and carpels.
- Complete Flower — has sepals, petals, stamens, and carpels.
- Monoecious — both male and female flowers on one plant.
- Dioecious — male and female flowers on separate plants.
- Superior Ovary — ovary above other flower parts.
- Inferior Ovary — ovary below other flower parts.
- Flower Formula — a symbolic representation of flower structure.
Action Items / Next Steps
- Observe flowers in your neighborhood and identify their parts.
- Practice writing flower formulas for observed flowers.
- Dissect a flower and examine its ovary and other structures (wash hands afterward).
- Prepare to discuss hibiscus pollination and variations in future classes.