Flowering plants are the most abundant plants on Earth with more than a quarter-million species taking a variety of forms, according to botanists Pam Soltis, Doug Soltis and Christine Edwards on Tree of Life website. Flowering plants are also the most advanced species in terms of evolution, which can be seen by observing differences in anatomy between them and nonflowering plants. These advancements have helped to make flowering plants the most successful plant species on Earth.
Unlike animals, plants produce their own food using energy from the sun to reorganize water and carbon dioxide molecules to form sugar in a process called photosynthesis. Photosynthesis goes on in the leaves in tiny cellular structures called chloroplasts. As illustrated on the website of retired Harvard professor John W. Kimball, leaves consist of multiple layers: an epidermis that limits evaporation of water from the leaves, a palisade layer where most photosynthesis occurs, a spongy layer for storing water and photosynthetic products and tiny pores called stomata that take in carbon dioxide and release oxygen.
Once photosynthesis occurs, plants face the challenge of transporting energy to areas far from the leaves where photosynthesis occurs. Furthermore, they need water from the ground to carry out photosynthesis--as well as numerous minerals--carried to distant leaves. In order to accomplish this, according to Dr. Kimball, flowering plants have vascular systems that move water from the roots to the leaves and photosynthetic products from the leaves throughout the plant. Unlike other plants, in flowering plants, the pipelines flowing from the roots to the leaves are long tubes of nonliving tissue that function like drinking straws, as evaporation from the leaves pulls water up from the roots. (See References 4)
Flowers consist of reproductive and non-reproductive structures. The nonreproductive parts of the flower, obvious when observing most flowers, are the petals and the sepals, leaves that protect the developing flower. Even though these structures do not produce sex cells or directly engage in reproductive function, their coloration attracts birds, bats and insects that carry pollen from plant to plant.
Within each flower as well are the reproductive structures. Most flowers contain both male and female structures. Male structures called stamens produce pollen, which contains sperm cells. The female structure is the pistil, where pollen lands and fertilizes the egg in the ovary at the base of the flower. The pistil generally arises from the center of the flower, while the stamens are arranged around it. Within the ovary are one or more ovules, each of which has the potential to become a seed.
As explained on the Seed Biology Place website, only flowering plants protect their seeds inside of an ovary. Once the egg is fertilized, a seed develops, along with other structures that aid in seed dispersal. Some flowering plants, for example, produce fruit, while others produce parachutes so that the seed can carry on the wind. Flowering plant seeds contain an embryonic plant with primitive leaves and roots, along with a nutritive substance called endosperm that the seedlings will use for nutrition as they begin to germinate.