Reproductive Strategies of Flowering Plants

Ragweed

• Ragweed (Ambrosia) contains numerous clusters of inconspicuous pollen-producing flowers at the tips of the spikes.

Reproductive Flexibility of Flowering Plants

• Flowering plants (angiosperms) include about 300,000 species. They reproduce both sexually and asexually.
• Flowers are adapted for sexual reproduction through varied colors, shapes, and fragrances to attract pollinators.
• Sexual reproduction involves the fusion of gametes (eggs and sperm cells) in the flower's ovary.
• Sexual reproduction results in genetically varied offspring, potentially better suited to the environment.
• Asexual reproduction produces offspring genetically identical to the parent plant, without flowers, seeds, or fruit.
• Offspring develop from vegetative parts like stems, leaves, or roots.

Flowers

• A flower is a reproductive shoot made up of four whorls of organs: sepals, petals, stamens, and carpels.
• Sepals protect the flower bud, often green.
• Petals attract pollinators, often colorful.
• Stamens produce pollen, with anthers containing pollen grains.
• Carpels contain ovules which develop into seeds.
• A complete flower has all four parts (sepals, petals, stamens, and carpels).
• An incomplete flower lacks one or more of these parts.
• A perfect flower has both stamens and carpels.
• An imperfect flower has either stamens or carpels, but not both (thus, an imperfect flower is also incomplete).

Pollination

• Pollination is the transfer of pollen grains (from the anther) to the stigma.
• Self-pollination occurs within the same flower, or a different flower on the same plant.
• Cross-pollination occurs between flowers on different plants of the same species.
• Animals (beetles, bees, flies, butterflies, moths) and wind can pollinate plants.
• Water pollinates some aquatic flowers.

Methods of Seed and Fruit Dispersal

• Wind
• Animals
• Water
• Explosive dehiscence

Seed Germination

• Seed germination requires water for activation of metabolic processes.
• Temperature, oxygen, and light are also environmental cues affecting germination.

Fruits

• Fruits are mature, ripened ovaries that protect seeds and sometimes aid in dispersal.
• Simple fruits develop from one or more fused carpels (e.g., berries, drupes)
• Aggregate fruits develop from multiple carpels in a single flower (e.g., raspberries, blackberries).
• Multiple fruits develop from multiple ovaries (and therefore multiple flowers) on a single stem (e.g., pineapples, figs).
• Accessory fruits are composed of both ovary tissue and other tissues, including floral parts (e.g., apples, pears).