Leaf Botany and Plant Cell Biology Part 2

Structure and Anatomy of Flowers Overview of Flowers • The primary purpose of a flower is sexual reproduction • The color and fragrance of a flower is the result of adaptive strategies ▫ They are only pleasing to humans as a coincidence of evolution Classification • Flowers, like leaves, are key to classification. ▫ This classification system, or Linnaean system, was developed by Linnaeus and is characterized by each species having a Latin genus and species name. • In flowers, the name is based on the flowers or other reproductive part of the plant ▫ This turned out to be a fortunate turn of events, as flowers are the part of the plant least affected by environmental factors • A knowledge of flowers is essential for anyone who will use plant ID as a part of their career. Flower Structure • The flower has both male and female organs. • The male organ is the stamen • The female organ is the pistil, but may also include the sepals, petals, and nectar glands. The Stamen • The stamen is the male reproductive organ • The stamen consists of the anther (pollen sac) and a long, supporting filament • The filament holds the anther in position, making it more available for birds, bees, or the wind to carry pollen away The Pistil • The pistil is the female part of the plant ▫ It is generally shaped like a bowling pin and is usually located in the center of the flower • The pistil consists of a stigma, style, and ovary ▫ The stigma is located at the top and receives pollen ▫ The style serves as a ‘neck’ connecting the stigma to the pistil ▫ The ovary contains the eggs which reside in ovules  If the egg is fertilized, the ovule becomes a seed. Petals • Petals are typically the colorful portion of the flower ▫ Collectively, the petals form the corolla • Below the petals are the protective leaf-like structures called the sepals ▫ Collectively, the sepals are called a calyx. Petals & Leaves • Petals and leaves are useful in determining whether a plant is a monocot or a dicot ▫ Monocots have parallel veins and flower petals that come in three or mutliples of three ▫ Dicots have net-veined leaves and flower petals in fours or fives Terminology • If a flower has a stamen, pistil, petals, and sepals, it is called a complete flower. • If one or more of these parts are missing, it is called an incomplete flower. • The male stamen and the female pistil are the most essential parts of the flower because they are involved in seed production ▫ If a flower has both functional stamens and pistils, it is called a perfect flower ▫ If either are lacking, it is imperfect How Plants Reproduce How Seeds Form • Pollination is the transfer of pollen from an anther to a stigma • A plant’s method of pollination can usually be determined by it’s color and odor ▫ Colorful, fragrant flowers are typically pollinated by animals or insects ▫ Wind-pollinated flowers tend to lack these traits Fertilization • When pollen reaches the stigma of the pistil, the stigma will release a chemical signal • This chemical signal will cause the pollen to grow a long tube • This long tube will travel down the style to the ovules inside the ovary • When the pollen tube reaches the ovary, it releases sperm cells, at which point fertilization should occur. • http://extension.oregonstate.edu/mg/botany/images/fertilization2.html Fruits • Fruits consist of the fertilized, mature seeds (ovules) as well as the ovary wall. • The seeds contain genes from both the male and female parts of flowers • The flesh of the fruit is genetically identical to the female plant Types of Fruit • Simple fruits arise from a single ovary ▫ Examples: apples, pears, tomatoes ▫ NOTE: a tomato is a fruit because it developed from a flower; vegetables are classified as coming from the roots, stems, or leaves of a plant • Aggregate fruits develop from a single flower with many ovaries ▫ Examples: strawberries, raspberries • Multiple fruits come from separate flowers with their own calyx and corolla on a single axil.