From Biol301

Contents 1 Angiosperms 1.1 Systematisits are Identifying the Angiosperm Clades 1.1.1 What Evolutionary Innovations Made Aborella so Fit? 1.2 The Flower is the Defining Reproductive Adaptation of Angiosperms 1.3 Fruits Help Disperse the Seeds of Angiosperms 1.4 The Life Cycle of an Angiosperm is a Highly Refined Version of the Alternation of Generations Common to all Plants 1.5 The Radiation of Angiosperms Marks the Transition from the Mesozoic Era to the Cenozoic Era 1.6 Angiosperms and Animals have Shaped one Another's Evolution 2 Plant and Human Welfare 2.1 Agriculture is based almost entirely on Angiosperms 2.2 Plant Diversity is a NonRenewable Resource

Angiosperms

• Better known as flowering plants
• about 250K known species
  • only about 720 known gymnosperm species

Systematisits are Identifying the Angiosperm Clades

• Angiosperms are in the phylum 'Anthophyta'
• we used to think there were just monocots and dicots, but then we found a group that is like dicots but split off before the split between mono and di cots.
  • So now we have monocots and eudocots (which is a clade including most of but not all of the dicots), and those other non-included dicots.
• It seems the most recent common ancestor to all the angiosperms is a plant called Amborella trichopoda which grows only in New Caledonia.

What Evolutionary Innovations Made Aborella so Fit?

• refinement of a vascular system (a network of vessels capable of moving water and such)
• There are three types of xylem in angiosperms:

1. tracheids: this xylem is a long tapered cell system that functions as mechanical support and water transport
2. fiber cells specialized for support
3. vessel element which are much like tracheids but shorter, wider, and laid end to end (not tapered). Also, they are not found in Amborella which suggests they developed later in the angiosperm line.

The Flower is the Defining Reproductive Adaptation of Angiosperms

• some flowering plants are wind pollinated and some are animal pollinated
  • often, flowering plants growing in large crowds are wind pollinated
• There are four types of specialized leaves:

1. Sepals: bottom leaves; often green; enclose the flower before it opens.
2. Petals: brightly colored (to attract pollinators); dull for wind pollinators.
3. Stamens: the male reproductive organs; produce microspores that give rise to male gametophytes; contain the filament, terminal sac, and anther (where gametes are produced).
4. Carpels: the female sporophylls; make megaspores; contain stigma (receives pollen), syle and ovary (which contains ovules which develop into seeds).

• Enclosing seeds in ovaries is one distinction between Angiosperms and Gymnosperms

Fruits Help Disperse the Seeds of Angiosperms

• A fruit is a mature (fertilized) ovary.
• Plants have been selected for ways to disperse their fruits: some make them sticky so animals take them with them not by choice, some make them tasty so the animals chooses to take it with them in their tummy.
• Fruit from a single ovary is called a simple fruit
  • Cherries, soybeen pod.
• An aggregate fruit is one resulting from several carpels.
  • Blackberries
• Multiple fruit forms from multiple flowers fused together.
  • Pineapple
• Wheat, rice, corn and other grasses are usually mistaken to be seeds. They are fruit with a dry pericarp (the outer-most, fleshy layer).

The Life Cycle of an Angiosperm is a Highly Refined Version of the Alternation of Generations Common to all Plants

• Pollen is the male gamete. It has two haploid cells in it.
• Ovules hold the embryo sac which is the female gamete.
• Often plants have mechanisms for ensuring cross-breeding.
• So a pollen sticks to the stamen and begins to grow. It grows down through the style to the ovule which it enters through the micropyle and inserts the two gametic cells into the embryo sac.
  • The embryo is now double fertilized making it 3n. Some believe this is to synchronize the development of the seed and its food storage methods.
  • As the seed develops it gains a rudimentary root and cotyledons (mini leaves; monocots only have one, dicots have two).
    • Monocots start storing energy reserves in the endosperm while dicots store theirs in the cotyledons.

The Radiation of Angiosperms Marks the Transition from the Mesozoic Era to the Cenozoic Era

• this was a rather useless section.

Angiosperms and Animals have Shaped one Another's Evolution

• Animals' need to eat causes them to pressure plants and vice versa. This is called coevolution.

Plant and Human Welfare

• We are completely dependant on plants for life when it comes down to it.

Agriculture is based almost entirely on Angiosperms

• Flowering plants provide nearly all our food.
• Corn, rice, wheat = grass fruits.

Plant Diversity is a NonRenewable Resource

• Slash-and-burn of tropical wildlife areas occurs such that in 25 years all the land will be cleared.
• Don't kill the forests...etcetera.