Angiosperms: Monocots and Dicots Overview

Angiosperms Overview

  • Angiosperms are flowering seed plants.
  • They are characterized by being sporophyte dominant.
  • Two major groups: Monocots and Dicots.

Monocots

  • Definition: Plants with one cotyledon (seed leaf).
  • Examples: Lilies, daffodils, tulips, palm trees, grasses (e.g., wheat, corn, rye, oats, bamboo).
  • Leaf Structure:
    • Veins: Parallel venation.
    • Embryos: Contain one cotyledon.
  • Roots: Typically have a fibrous root system.
  • Floral Parts: Usually in multiples of three.
  • Vascular Bundles: Arranged in complex patterns scattered throughout the stem.

Dicots

  • Definition: Plants with two cotyledons (seed leaves).
  • Examples: Deciduous trees, bushes, various vegetables, field flowers, garden flowers.
  • Leaf Structure:
    • Veins: Netlike venation.
    • Embryos: Contain two cotyledons.
  • Roots: Typically have a taproot system.
  • Floral Parts: Usually in multiples of four or five.
  • Vascular Bundles: Arranged in a ring pattern in the stem.

Dicot Leaf Anatomy

  • Structures:
    • A: Palisade mesophyll
    • B: Spongy mesophyll
    • C: Epidermis (upper and lower)
    • D: Stomata (pores for gas exchange)
    • E: Guard cells (control the opening/closing of stomata)
  • Note that A + B = mesophyll, where photosynthesis occurs (contains chloroplasts).

Dicot Leaf Example (Privet)

  • Review of anatomical structures found in the Dicot leaf anatomy.

Monocot Leaf Anatomy

  • Structures:
    • A: Bulliform cells help curl the leaf to reduce water loss in drought conditions.
    • Includes vascular bundles and epidermis.

Leaf Adaptations

  • Water Lily: An aquatic plant characterized by:

    • Increased air space in spongy mesophyll.
    • A: Sclerids, which provide structural support.
    • Stomata located on the top surface since the leaf floats on water.

  • Oleander: Adapted to dry environments:

    • Thick epidermis aids in water retention.
    • A: Stomatal crypts with trichomes (hairs) that help reduce water loss.

Stem Anatomy

  • Dicots:

    • Herbaceous dicot stem (e.g., sunflower):
    • A: Pith (parenchyma tissue).
    • Vascular bundles arranged in rings with xylem (X, purple) and phloem (P, blue-green).

  • Monocot:

    • Stem example (corn):
    • Scattered vascular bundles with Xylem (X) and Phloem (P).

  • Woody Dicot Stems:

    • Growth over the years:
    • Year 1: Formation of wood and bark.
    • Cambium layer produces secondary xylem, increasing the girth of the stem.
    • Seasonal changes: Spring xylem vs. Summer xylem.

  • Vascular Bundle Functions:

    • Xylem: Transports water and minerals.
    • Phloem: Transports nutrients and sugars.