There are four major groups of plants: non-vascular, vascular, gymnosperms, and angiosperms. Each is unique in structure, function, and environmental needs.
Non-vascular plants, as stated in the name, lack a vascular system. A vascular system is a set of well-developed vascular tissues that helps distribute materials efficiently within a plant. Because non-vascular plants have no true way of transporting materials and substances, they are often very small in size, like mosses, liverworts, and hornworts. They also lack true roots, stems, and leaves, although they often have structures that look like them. They posses large gametophytes, held to the surface which they grow on by rhizoids (hair-like projections). The sporophytes grow on top of the gametophytes and depend on them for nutrients. Non-vascular plants also need to be covered by water before fertilization can occur, so that the reproductive cells can easily make it to neighboring plants.
Non-vascular plants are also tough and hardy, and can be found growing in odd places, such as on rocks. The only environmental requirement is that there must be moisture, even in a small amount. When moisture gathers in the cracks and crevices on a rock, that makes it sufficient enough for moss to germinate. More often than not, though, you’ll find non-vascular plants need a damp environment, like along a riverbed or coastline.
Vascular plants can be seedless, just like non-vascular plants. Some early vascular plants had horizontal underground stems called rhizomes. Vascular plants clearly have a vascular system with two types of transportation cells, called xylem and phloem. Xylem transports water and minerals, while phloem takes care of the plant’s organic nutrients. Vascular plants also have larger, more complex sporophytes, enabling them to reach great sizes and have cell specialization. They are even drought resistant. The smaller gametophytes of seedless vascular plants develop under the soil. Water is necessary for fertilization, as with non-vascular plants. Some examples of these seedless vascular plants include club mosses, horsetails, and whisk ferns.
Gymnosperms are seed plants with a vascular system, and they do not carry fruit. Instead, they carry cones, in which male and female gametophytes respectively develop in male and female cones. The gametophytes form inside the sporophytes; grains of pollen are male, and females form within structures that become seeds. They are also pollinated by the wind, and because of this can even reproduce when conditions are very dry. Examples of gymnosperms include conifers, cycads, ginkgoes, and gnetophytes.
Angiosperms are the final group and make up the majority of seed plants. They posses flowers and sometimes fruit, created to protect the seed. Both male and female gametophytes develop within flowers, and bright colors and strong scents attract insects and other animals. This allows pollen to be carried very long distances and can increase the chances of cross-pollination. Fruits, like melons and apples, are sometimes produced to protect the seeds within. If an animal consumes the fruit, the seeds can pass undigested through the animal’s system and then germinate. Some seeds are carried by wind or water. Angiosperm seeds carry endosperm, which is stored food for the developing plant embryo. Angiosperms are further classified by scientists in two groups: picots and monocots. They are distinguished by the number of cotyledons (seed leaves) produced. Simply, monocots produce one, and dicots produce two. Both will eventually produce flowers.
Johnson, George and Peter Raven. “Biology” Holt, Rinehart, and Winston, 2006. Print.