Seed plants (Division Spermatophyta) are the most common plants on earth today. In the fossil record, there are examples of now extinct tree ferns that had seeds, indicating seed plants likely originated from ferns. Seedless plants reproduce via spores, which are single-celled zygotes with a tough cell wall. Seed plants reproduce via seeds, which are multicellular structures with a tough exterior tissue (seed coat) encompassing an embryonic plant. Seeds also typically have nutritive tissue within the seed coat used to nurture the embryo during its dormancy and early development, while spores have no nutritive tissue.
Extant seeds plants are divided into two large groups: gymnosperms and angiosperms. Gymnosperm translates to “naked seed,” meaning that the seed is not enclosed in a protective structure. Gymnosperms include conifers, cycads, ginkgos, and the perplexing gnetophytes. Angiosperm translates to “vesseled seed,” in which the seed is encased in a protective structure, called fruit. It is important to note that not all fruits are fleshy. For example, peanuts are encased in a hard shell. The shell is actually the fruit, where the peanut is the seed. Angiosperms are composed of two classes, Magnoliopsida (dicotyledons) and Liliopsida (monocotyledons), and include all the flowering plants, from roses to lilies and even grasses.