Seed Bearing Plants
- According to Estrella Mountain Community College, the plant kingdom contains over 300,000 different species of seed and nonseed-bearing plants. Angiosperms and gymnosperms make up the two broadest categories of seed-bearing plants. According to the Canadian Encyclopedia, plants developed seed structures anywhere from 250 to 300 million years ago. Prior to their development, plants were restricted to water-based environments due to their inability to reproduce without the aid of a water or moisture-based medium. The development of seeds provided a more reliable reproductive process and made use of other more diverse methods of fertilization.
- According to Estrella Mountain Community College, plant evolution came about through changes in their reproductive processes. Reproduction in all plants follows an alternation-in-generations cycle where stages involving spores and sex cells alternate from generation to generation. Prior to the arrival of seed-bearing varieties, the spore stage was the primary means for reproduction. As spores required water for fertilization to take place, these plants could only survive within water-based environments. Seed development came about as plants began to incorporate both the spore and sex cell stages within their reproductive process.
- Along with the change in reproduction processes came the development of specialized, vascular tissue structures capable of conducting water throughout plant structures. The development of vascular tissues made it possible for plant bodies to conduct needed water and nutrients from water and soil-based environments up into the plant's structures. This development enabled plants to stand upright and survive within land or soil-based environments. This, coupled with their ability to bear seeds, made it possible for plants to create a variety of land-based living environments, like forests and woodlands.
- According to the Canadian Encyclopedia, gymnosperm plants and trees make up the group of plants that have no covering on their seed structures. Instead, seeds or ovules are contained inside female cone structures that sit on the outside of the leaves. Male cone structures--also situated on leaf surfaces--produce pollen grains, which fertilize the ovules. Fertilization, or pollination takes place when wind currents blow pollen grains into female cone structures. As wind is the only method for fertilization, gymnosperms are limited in their ability to branch out into new environments.
- Angiosperms include the flowering varieties of plants and trees. According to the Canadian Encyclopedia, this category of seed-bearing plant carries its reproductive structures inside the flower portion of the plant. Angiosperm seeds are characterized by a covering that protects seed ovules as well as provides nutrient materials to developing embryos. Flower structures also promote additional methods for fertilization through their colorings and scents by attracting insects and animals. Pollination can take place over large distances as insects and animals transfer pollen grains from plant to plant. As a result, angiosperms are the most abundant and diverse species of plants.