Seed plants, Spermatophyta, make up about 350,000 species of plants in the plant kingdom. They include trees, bushes, grasses, herbs, vines, ferns, mosses, green algae and flowering plants. These organisms propagate by producing a seed and are great contributors to the resources of the earth.
The first primitive seed plants, Pteridospermae, or "seed ferns," appeared in the late Devonian period. They once populated forests but diversified so much over the ages that they are now extinct.
Seed plants are broken down into two major groups. Gymnosperms have exposed seeds and include conifer trees such as pines, spruces, cedars and redwoods. Angiosperms have seeds covered by a fruit and include all flowering plants.
Seed plants are well-adapted to land as opposed to mosses and ferns, and their sperm do not require water for survival and reproduction. Reproduction takes place through pollination.
Seed plants are heterosporous--they have two different spore sizes representing the male and the female gametophyte. They also have a seed that protects the embryo until it is ready to develop. Seed dispersal enables the embryo to secure a growing spot away from the mother plant.
Seed plants benefit the environment by changing carbon dioxide into oxygen through the process of photosynthesis. They also contribute to the earth's resources by producing food, wood and other important items.