Variations on gametophyte/sporophyte relationships

Angiosperms

• a.k.a flowering plants
• are seed plants that produce reproductive structures called flowers and fruit
• most widespread and diverse of all plants

Angiosperm Evolution

• first appeared during Mesozoic~140 MYA
• by the end of Mesozoic~65 MYA, angiosperms dominated many landscapes
• Coevolution between plants and animals very important!
  • herbivores, pollinators, and seed dispersers

Mostly male hypothesis

• Angiosperms evolved from male gymnosperms
• Pollen and ovule producing structure mutated into single structure
• mutation:ovules developed on microsporophylls/carpels
• evidence: flower development genes are similar to pollen producing gymnosperm genes
• position of ovules can be easily changed with mutation

Traits of Angiosperms

• vascular seed plants that produce flowers and fruits
• extremely diverse~120,000 species
• Xylem has tracheids, fibers, and vessel elements!
• life cycle includes double fertilization

Flowers

sepals-enclose the flower

petals-brightly colored to attract pollinator

stamen-produces pollen

carpel-produces ovule

Structure of a Flower

Bisexual

perfect flowers have both stamens and carpels

Inflorescence

composite flowers, on a common stem or peduncle

sunflowers have ray flowers and disc flowers

Monocots-single cotyledon, parallel veins, fibrous roots, flowers in sets of 3's, and scattered vascular tissue

Eudicots-two cotyledons, net-like venation,tap root system, flower in set's of 4's and 5's, and vascular tissue arranged in a ring

Disadvantages of Sexual Reproduction

• only half of the population can produce offspring
• sexual structures are costly
• pollination can be difficult if pollinators/wind is not available
• sex can break up successful genotypes, offspring may be less suited to environment than parents

Ways to reproduce without sex

Self pollination-involves meiosis and fertilization, offspring from "selfing" are genetically very similar to parent

Asexual reproduction-only mitosis involved, offspring are clones of the parent

Mechanisms for avoiding self pollination

1. Being dioecious &female parts on two plants
2. In monoecious plants, with separated female and male flowers, the flowers mature at different times or are physically separated
3. Dichogamy:stamens and carpels mature at different times on the same flower
4. Stamens and carpels are physically separated in the same flower
5. Genetic self-incompatibility: pollen will not successfully fertilize when it recognizes itself

Wind Pollination

• May be advantageous in habitats that lack reliable animal pollinators
• More common in open habitats and at higher elevations, with low humidity and rainfall
• Feathery stigmas and long stamens
• Pollen grains are small, abundant, and smooth. 
• Flowers usually lack nectar, fragrance, petals, and are unisexual
• Most grasses and many trees use it

Biotic Pollination

• only advantageous in habitats that have reliable animal pollinators
• common in wide variety of habitats
• simple stigmas and variable stamens
• pollen less abundant, variable in size, and often with elaborate ornamentation
• flowers usually have nectar,fragrance, a showy perianth, and are usually bisexual

Pollinator Syndrome

flowering plants species evolve specific morphologies that attract certain pollinators

• hummingbird-red, odorless with long corrolla tube and lots of nectar
• bat or moth- white, with strong odor emitted at night
• bee- brightly colored yellow or blue petals with distinct markings and a landing platform.
• fly-pollinates dark brown color with foul odor (like rotting flesh)

Why double fertilization?

Double fertilization synchronizes development of food supply (endosperm) with development of embryo: if no fertilization occurs, no resources are wasted. 

Life Cycle of Angiosperm

Gymnosperm vs. Angiosperm Seeds

Fruit and Seed Dispersal

• Fruit protect seeds during development and sometimes aid in dispersal
• Fleshy fruits and seeds are adapted to animal dispersal
• Dry fruits can be adapted to air or water dispersal, animal dispersal, or to release seeds at maturity
• Seeds themselves often have their own dispersal adapted morphology, and adaptations for survival and germination

Development of Dicot Embryo