4) Reproduction and Development in Flowering Plants

Flowering plant “identity”

• Angiosperms = flowering plants

• Key innovation = flowers

• Flower organs explicitly pointed out:

  • Stigma

  • Ovary (containing egg(s))

  • Anther(s)

Pollination syndromes (lecture emphasizes this as a flower innovation)

• Slide states: “Flowers – key innovation: pollination syndromes”

• Core interpretation:

  • Pollen movement mostly shorter distance (pollination syndrome)

  • Seeds disperse potentially long distance (seed dispersal syndrome)

Double fertilization (ANGIOSPERMS ONLY) + why it matters

• Seed anatomy lecture explains:

  • Endosperm = food storage cells in seed

  • Not part of embryo

  • Developed through Double Fertilization (DF)

• Mechanism (must memorize steps + ploidy):

  • Pollen fertilizes egg → embryo (that’s the “regular” fertilization)

  • One pollen nucleus (1n) fertilizes the central cell (2n) → endosperm (3n)

• Concept: endosperm food supports embryo until cotyledons can photosynthesize (when cotyledons are green)

Seed anatomy and early development (high yield)

• Seed contains:

  • Embryo, covered by seed coat/testa

• Embryo parts:

  • embryonic shoot

  • embryonic root (radicle)

  • cotyledons (embryonic leaves)

• Food sources:

  • Endosperm (for embryo)

  • In some cases “food for disperser” shown on diagram

Endosperm vs cotyledons as storage (important comparison)

• Some seeds keep endosperm as main reserve (example slide shows castor bean, corn)

• Many angiosperms absorb food early into cotyledons:

  • Cotyledons store food → may be fat/white, may not photosynthesize at first

• Cotyledons later replaced by first true leaves (diagram)

Seed dispersal (selected mechanisms shown)

• “Myrmecochory” listed (ant dispersal)

• Barochory + small animal dispersal notes:

  • big heavy seeds (starch/oil-rich)

  • caching → some forgotten → seedling recruitment

• Dispersal distance comparison ranges from meters to hundreds/thousands of km on the slide

Development patterns: monocots vs eudicots (lecture 7)

• Angiosperms largely divided into:

  • Monocots (1 cotyledon)

  • Eudicots (2 cotyledons)

• Differences to memorize:

  • Leaf venation: monocots parallel, eudicots net/branched

  • Roots: monocots fibrous, eudicots tap root

  • Floral parts: monocots in 3’s, eudicots in 4’s or 5’s

  • Vascular bundles: monocots scattered; eudicots arranged in a circle

  • Woody potential: secondary growth mainly in woody eudicots (and conifers); monocots typically herbaceous (reason: can’t connect scattered bundles into a ring)