Category: 2. Angiosperms Flowering Seed Plants (Covered Seed Plants)

Beyond ornamental uses, flowering plants constitute much of what we eat, parts of the clothes we wear, the wood in our homes and furniture and the medicines we consume. Flowering plants are everywhere and thus have a million uses. All fruit comes from flowering plants, obviously, and think of how many just in the edible category there is, not to mention all of those that aren’t for eating. Stop and think for a minute on the plants that you encounter in daily life, chances are good they came from a flowering plant.

Specializations in flowering plants include an overall efficiency in plant growth. Flowering plants may be classified in various ways: by the number of parts, the fusion of parts, the appearance of compound pistils that are composed of several carpels, various positioning of the ovary with respect to the receptacle including inferior and superior ovaries, and irregular flowers and unisexual flowers. A monoecious species of flower has both male and female flowers on the same plant whereas a dioecious flower would have separate plants for male and female flowers. All of these are characteristics that can be looked at in the classification and categorization of flowering plants.

Some fruits can develop without the development or the fusion of gametes. These fruits are called parthenocarpic fruits. Not all ‘seedless’ fruits are parthenocarpic.

The pollen grain contains two sperm nuclei (formed from a generative nucleus that splits) and one tube nucleus. The tube nucleus forms a pollen tube that grows through the stigma, the style and into the ovary via the micropyle. Upon arrival at the ovary, one sperm nuclei will fertilize the egg and form a zygote. The other sperm nuclei will fuse with the polar nuclei of the egg in order to form a 3n endosperm nucleus. This will be conserved as food for the plant embryo or may become part of the seed. Some species will end up with 5n, 9n, or 15n endosperm tissue, depending on how the embryo sac develops.

The process of transferring pollen grains from the anther to stigma is called pollination. This may occur via wind, insects, birds, or other agents. Flowers may be geared toward certain pollinators. For example, flowers pollinated by bees are usually sweet and fragrant. Their colors are usually blue and yellow. Beetles are attracted to flowers with strong odors and dull colors or white flowers. There are fly-pollinated flowers that smell like rotting meat. Moths are drawn to pale yellow or white flowers. Birds, akin to bee preferences, like sweet nectar and fragrant flowers with bright colors. Orchids have unusual pollination mechanisms, and in some, they literally grab an insect and manually attach two pollen packets to the hind end of the insect before releasing it.

Angiosperm gametophytes develop in separate structures, sometimes on the same plant. The embryo sac, or female gametophyte, develops in the ovule which is surrounded by integuments. The integuments will later become the seed coat after fertilization has occurred. The male gametophytes, pollen grains, develop in the anthers.

Angiosperms are plants that have seeds encased in a protective covering. That covering is the ovary; it is the part of the flower structure. It distinguishes angiosperms from gymnosperms, the other seed plants. So it can be said that angiosperms are also flowering plants. The angiosperms may be divided into two classes: monocots and dicots. Angiosperms, like gymnosperms, are heterosporous, which means they produce two types of spores and their sporophytes are more dominant than those of gymnosperms. At maturity, the female gametophytes are reduced to a few cells and are completely enclosed within sporophyte tissue; while the male gametophytes consist of a binucleate cell with a tube nucleus which forms a pollen tube much like the one formed in gymnosperm pollination.