Plant Reproduction and Diversity

• Mostly multicellular photosynthetic autotrophs
  • Primary photosynthetic pigments = Chlorophylls a, b
• Many possess vascular tissues for transport of water and nutrients

• All sexually reproducing organisms have an alternation of generations
  • the organism passes through a haploid and a diploid stage in their life cycle
  • in humans, for example, the diploid state is us; the haploid state is the gamete (sperm and egg). All the machinery for producing the gametes is contained within the individual.
• In plants, however, the machinery for producing gametes is not always contained within the individual.
  • Haploid - gametophyte, produces gametes (then syngamy)
  • Diploid - sporophyte, produces spores (meiosis)
• Primitively, the haploid state is the dominant stage
  • the diploid is only briefly seen
• However, as plants evolved, the diploid state became more dominant

Plants with dominant haploid stages

• Diverse morphology (solitary, colonial, multicellular)
• Aquatic (usually fresh water)
• Even though the chlorophytes are more the sister taxa to the terrestrial plants, they are often placed in the Kingdom Protista. This is incorrect in a phylogenetic context.

• "Amphibians of the plant world."
• No vascular tissue.
• Only gametophyte is photosynthetic (free-living).
• Sporophyte is a parasite
• How do they deal with life on land?
  • They are small, low to the ground, only grow where moist.
• What are some limitations to this life-style?
  • Reduced environmental tolerance. Poor genetics (haploid dominant)

Plants with dominant diploid stages

Lycophyta (lycopods)

• free-living sporophyte and gametophytes
• leaves and roots different from other land plants
• in the geologic past (ca 300 MYA), the lycopods were the dominant floral elements with large, expansive swamp-forests of lycopods. Much of the coal and oil found today were formed from the extensive growth of these plants

• free-living sporophyte and gametophyte
• no leaves or roots
• three-lobes spornangia
• one known genus survives today, but they were much more diverse in the past
  NOTE even though they are called "wiskferns," they are not true ferns

• free-living sporophyte and gametophyte
• circular, ribbed stems with whorled leaves
  again, much more diverse in the past

• free-living sporophyte and gametophyte
• vascular tissue
• by far the most diverse non-seed land plant today
• Review life cycle:

What adaptations are present which make it more adapted to life on land?

• Vessels, larger leaves, taller

• Need water for gamete transfer.

• Gametophyte very vulnerable. Still require some moisture.

The evolution of pollen and seeds

• Gains - protection of gametophyte
• Losses - more stress on the sporophyte

	Pollen - male gametophyte, protected by a spore wall (protects from harsh environment) Gain - protection Loss - need some mechanism to carry pollen (air, insects)
	Ovule - contains the female gametophyte (the egg sac), protected by sporophyte  tissue (the integument - this becomes the seed coat) Gain - protection Loss - extra care for sporophyte
	Seeds - baby plant in a box with its lunch The seed is one of the most distinct adaptations in the plant world The young sporophyte no longer needs to grow and photosynthesize immediately (can go dormant). Can be dispersed (air, animal vector) The plant produces food for each ovule, in the hopes that it will be fertilized Gain - protection, dispersal, dormancy Loss - great energy cost to plant

• Pollination by wind and insects. Pollination can take up to 10 years.
• Seeds eaten by birds - poisonous to humans (causes slow, degenerative. brain disease)

• Wind pollination - lots and lots of pollen produced
• Produce cones w/ ovules - two year cycle
• Taxus and others can produce fleshy arils which are edible by animals
  • dispersal strategy similar to angiosperms with fruits

• Only one species kept alive in monasteries
• Very resistant to disease and pollution - often planted in cities
• Stinky seeds

• Double fertilization.
  • Allows for diversification
  • Acts as a signal to produce food only when fertilized - no more baby food before the baby!
  • Pollen sperm with two nuclei - one for fertilization of egg, one for polar bodies
  • Much more rapid life cycle
• Coevolution with pollinators - insects and plants (pollen dispersal)
  • Possess flowers to attract pollinators
• Coevolution with larger animals - mammals/birds and plants (seed dispersal)
  • Possess edible fruits and seeds to attract dispersal organisms

Sepals, petals, stamens, carpels Pollination Pollen tube Carpel w/ closed ovary

Fruits

• A fruit is a ripened ovary - it contains the seeds
• Often the fruit is edible - why would this be advantageous to a plant?
• There is a wide variety of fruit types - but all fruits are basically formed from a ripened ovary

• A seed is a ripened or mature ovule
• Often the seed is edible - this serves the same function as do edible fruits
• There is a wide variety of seed types

• A vegetable is an edible part of a plant that is not part of the reproductive organs (edible roots, stems, leaves, etc.)
• We will look at various examples of fruits, seeds, and vegetables in class - do not go by what you would call them in the supermarket

• Insects as pollinators - directional vectors
• What are the advantages and disadvantages of this arrangement?
• Weak coevolution vs tight coevolution

• Verts as seed dispersal
• What are the advantages and disadvantages of this?

Click here to view a simplified phylogeny of the kingdom Plantae