Week 3 | Day 2 | BIOA02

Week 3 | Day 2 | BIOA02

Generalized Flower Structure

Male parts:

  • Stamen (anther + filament)

Female parts:

  • Carpel (stigma + style + ovary)
  • Pistil (multiple carpels)

What Are Flowers?

  • Evolutionary, flowers are just modified leaves

Flower parts

Sepals

  • Commonly used to protect flower before the bud opens
  • Usually green
  • Can be free or fused to form tube

Petals

  • Typical colours to attract pollinators
  • Can be free or fused to form tube (as well)

Stamen (male)

  • Pollen producing
  • Anther: commonly 4 pollen sacs

Carpel

  • Stigma
    • Sticky landing platform for pollen
    • Has many shapes + sizes
  • Style
    • Connects stigma with ovary (basically a tube)
    • Style epidermis produces mucus for the pollen to go down (like a throat kind of)

Number of Parts in the Female Reproductive System

  • Flowers can have many carpels
  • Ovary can have many ovules
  • Ovule only has one egg cell
  • One ovary with one ovule
    • Eg. cherry, peach, olive
  • One ovary with many ovules
    • Eg. cucumber, tomato, melon
  • Flower with many carpels
    • Eg. blackberry, raspberry

Generalized Flower Structure

Four whorls:

  1. Sepals (0-3-4-5-many)
  2. Petals (0-3-4-5-many)
  3. Stamen (0-many)
  4. Carpel (0-many)
  • Basically, plants may not even produce stamen or carpel at all, and that helps diversity (I assume to prevent self-incest)

Partially Missing Reproductive Organs

  • Complete female: both male and female reproductive organisms (hermaphroditism)
    • 75% of angiosperms are this (eg. trillium, raspberry, evening primrose)
  • One individual: either male or female for each flower (not both on one flower) (monoecy)
    • 17% (eg. corn, hazelnut)
  • Individual: One individual either makes all female or all male (dioecy)
    • 6% (eg. hemp, asparagus)

More Varied Plant Reproduction

Dioecy

  • Outcrossing (one plant to another)

Monoecy

  • Selfing (to another flower)
  • Outcrossing

Hermaphroditism

  • Selfing (to the same flower)
  • Selfing (to another flower)
  • Outcrossing

Inbreeding Avoidance

  1. Temporal separation (time)
  2. Spatial separation (physical)
  3. Self-incompatibility (carpel can recognize if pollen that falls on it is its own)
  4. Temporal separation
  • Female phase develops first when young then turns into male
    • Stigma grows, then withers + makes way for anthers to develop
  • This method is good for selfing within a flower, but not for the whole plant (since it’s not always synchronous)
  1. Spatial separation
  • This method is not perfect but effective to some degree

Special Type of Spatial Separation

  • Spatial reciprocity
  • Main example primrose production