Seeded Plants: Angiosperms

Overview of Angiosperms

• Latin "Angio - sperm" = contained seed
• enclosed fruit
• Flowering plants
• Single phylum
• Anthophyta
• "Anthos" = flower
• largest taxa of seed plants
• Includes smallest and tallest of seed plants
• Reproduction
• Flower and Fruit: novel adaptation
• Most widespread and diverse of plants
• Monoecious: Male and Female parts together on same plant
• Dioecious: Male and Female parts on separate plants

Evolution of Angiosperms

• Non-Vascular Plants (~475 MYA; Paleozoic)
• Seedless Vascular Plants (~420 MYA; Paleozoic)
• Gymnosperms (~300 MYA; late-Paleozoic)
• This is when angiosperms split from gymnosperms (~300 MYA)
• Angiosperms (~145 MYA; mid-Mesozoic)
• Cretaceous Period: (140 - 70 MYA)
• Lots of Angiosperms
• Decline of Gymnosperms
• Related to Bennettitales: extinct seed plants with flower-like structures

• Darwin
• Sudden appearance of angiosperms was a mystery
• No obvious pre-cursers to flowers
• possibly because flowers are soft tissue, hard to preserve (fossil)
• Modern evidence shows angiosperms evolved from gymnosperm-like ancestors

Angiosperm Reproduction

Angiosperm Structures

• Flowers: modified leaves (sporophylls)
• Sepal and Petals: attract pollinators, non-reproductive
• Stamen: filament + anther
• Produces Microspore => male Gametophyte => pollen grain (sperm)
• Anther: produces the pollen
• Pistil: stigma + style + ovary
• Produces Megaspore => female Gametophyte => egg
• Each has 1 stigma, but may have many ovules

Angiosperm Life Cycle

• Anther produces the male gametophyte (pollen)
• Ovule produces the female gametophyte (megaspore)
• Pollen lands on stigma
• pollen tube grows into ovary
• Double Fertilization: Pollen tube releases 2 sperm
• 1 sperm fertilizes egg
• 1 sperm initiates development of endosperm: stored food
• Triploid Endosperm: 1 sperm + 2 female nuclei combine

Advantages of Angiosperm Reproduction

• Costly endosperm only created after successful fertilization
• Female gametophytes are smaller (cheaper and faster to produce) Recall: much less costly than moss or fern female gametophytes
• Fruit: Mature ovary with seed
• May look very different from original plant
• Protects dormant seed
• Attracts animals - aids in dispersal
• Types of seed dispersal
• Wind: seed has "wings"
• Adhesive: seed can stick (plants or animals)
• Fleshy: seeds are tasty, eaten by animals

Importance to humans

• Large portion of human diet
• 80% of calories from just six species
• Wheat
• Rice
• Corn
• Potatoes
• Cassava
• Sweet Potatoes
• Typically all parts are edible Examples: Seed, Fruit, Leaves, Roots, Tubers, Flowers
• Grown for other culinary purposes Examples: Oil, Spices, Flavoring, Sugar
• Drugs
• Medicinal
• Recreational

Angiosperm Pollination

• Gymnosperms mostly wind pollinated
• Angiosperms 80% pollinated by animals
• Some completely dependent on animals
• Evolved mechanisms to attract pollinators
• Bright flowers: daytime, visual attraction
• Smelly flowers: nighttime, usually colorless
• Co-Evolution (plant + pollinator)
• Reciprocal relationship: diversification of plants occurred at the same time as pollinator diversification
• Both exert selective pressures on each other (selective agents)
• Co-evolve
• Symbiotic Relationship:
• Plants spend less energy producing less pollen
• Instead, plants produce flowers, nectar etc. to attract pollinators to spread gametes
• Pollinators receive nectar / pollen (food)

Darwins Orchid Example

• Moth pollinated plant
• Plant has long tube to access nectar
• Moth's tongue was not long enough, so it rubbed its face against pollen (thus spreading pollen between plants)
• Moth evolved longer tongue to reach nectar more easily
• Plant responded by evolving longer tube
• Cycle continues until both species have exaggerated traits
• Also an example of Directional Selection