Angiosperms

Division Magnoliophyta: The Angiosperms

• Vascular plants possessing flowers, fruits & seeds
• Most successful plants today
• Reproduce sexually by producing seeds within fruits
• Have extremely well developed vascular systems
• Extremely important to humans
• All major human food crops are angiosperms

There are 2 major classes of angiosperms

• Class Liliopsida: The Monocots
• Class Magnoliopsida: The Dicots
• Differ in leaf structure, seed structure, vascularization, & flower structure

The Monocots:

• Monocots are Herbaceous (non woody) plants
• Stems have characteristic vascular system
• Leaves have parallel veination (veins run parallel to each other)
• Flower parts of a monocot occur in multiples of three.
• Seeds have a single cotyledon (embryonic seed leaf) and have endosperm (nutritive tissue)

The Dicots:

• May be herbaceous or Woody.
• Leaves are usually broader and have Netted Veination.
• Flower parts occur in 4 or 5's (or multiples of)
• Seeds have two cotyledons, and usually no endosperm.

Seed types

Stem Types

The Flower:
Flowers have 4 main organs

• Sepals
• Petals
• Stamens
• Carpels (or pistils)

• Flowers which have all 4 parts are called Complete
• Flowers lacking 1 or more parts are called Incomplete

• The main reproductive structures are the stamens and carpels (or pistils)

• Stamens are the male part of the flower
• Composed of 2 parts
• Anther
• Filament
• Contain microspore mother cells which produce microspores which develop into pollen grains

• Pistil or Carpel is the female part of the flower
• Composed of 3 main parts
• Stigma
• Style
• Ovary
• Ovary contains one or more ovules. Each ovule contains a female gametophyte

Life cycle of the flowering plant

• Each ovule contains a megasporocyte which undergoes meiosis to produce 4 haploid megaspores.
• Three disintegrate, the 4^th divides by mitosis to produce a female gametophyte.
• The gametophyte is composed of 8 haploid nuclei. Including:
• 1 egg
• 2 polar nuclei

• The pollen grain is formed from the microspores produced in anther.
• Consists of:
• Tube nucleus
• 2 sperm nuclei

Fertilization:

• Pollen grain pollenates flower
• Tube nucleus develops a pollen tube into the ovule.
• Here unique process of Double Fertilization occurs.
• One sperm nucleus fertilizes the egg forming a zygote.
• This develops into the plant embryo.
• Other sperm nucleus fuses with the 2 haploid polar nuclei to form a TRIPLOID (3N) nucleus.
• This develops into the endosperm of the developing seed.

Double fertilization