Angiosperms: Vascular Plants with “Flowers” Help
Introduction to Angiosperms (Vascular Plants)
The gymnosperms, as we have seen, are vascular plants that reproduce by means of spores and seeds. The seeds are naked, and they are usually attached along the exposed edges of female cones.
What is an Angiosperm?
Now we will examine the angiosperms ( AN -jee-oh- sperms ). These are the second major group of vascular plants, and they are named after an important part of their anatomy. These plants have “seed” ( sperm ) “vessels or holders”( angi -), meaning that their seeds are not naked. Rather, their seeds are enclosed within fruits. The angiosperms are also the true flowering plants, because their immature seeds are fertilized through a particular part of the flowers.
First Vascular Plants
The angiosperms probably first appeared on Earth during the Mesozoic Era, along with the gymnosperms, dinosaurs, and small mammals. [ Study suggestion: Go back and review Table 3.1 in Chapter 3 to help you keep these evolutionary developments in perspective.] During these early days (245 million to 65 million years ago), the planet was carpeted with ferns (nonvascular plants) and conifers (seedless vascular plants).
As time wore on, however, the angiosperms (vascular plants with fruit-covered seeds and/or flowers) began to take over. How were they able to do this? The angiosperms (with flowers) had a unique reproductive advantage over the gymnosperms (without flowers). The advantage was the help of the insects, such as bees, moths, and butterflies, which go from plant to plant and assist with pollination. Further, certain animals (such as bats) and birds (for example, hummingbirds), also help pollinate flowering plants. Fruits, by encasing their seeds, also assist the angiosperms in surviving and spreading. Now, within the Cenozoic Era, where we stand today (65 million years ago up to the present), the angiosperms have clearly become the dominant group of plants. There are about 275,000 species of flowering plants known, making them the most abundant and widespread, by far.
The Basic Anatomy Of A Flowering Plant
Figure 9.5 reveals the basic structure of a flowering plant. Most critical, of course, is the anatomy of the flower, itself. A flower is the reproductive portion of a plant, the portion that produces the seeds. Anatomically speaking, a flower is a specialized body of modified leaves located at the end of a pedicle ( PED -uh-kul), a “little foot-like” stalk. The surface of this pedicle, like the rest of the plant stem, leaves, and young roots, is covered by an epidermis ( ep -ih- DER -mis). The word, epidermis, exactly translates to mean “(something) present upon the skin.” In humans, the epidermis is the paperthin outermost layer of the skin. In ferns and seedbearing plants, the epidermis is an extremely thin layer of outer protective cells.
In the center of the flower (which lacks an epidermis), lies the ovary ( OH -vah- ree ). It is the oval-shaped “egg” ( ov ) producer. [ Study suggestion: Visualize a skinny human leg, covered by epidermis and sticking up into the air. At the top is the little foot, which has a deep downward curve on its sole. In the middle of the curve sits an egg. After you have visualized, check with the cartoon analogy and appropriate flower structures shown in Figure 9.5.]