Plants can be classified into several groups based on their structure and physiology. There are two major groups: non-vascular plants which lack vascular tissues for transporting water and nutrients, and vascular plants which have vascular bundles. Vascular plants are further divided into seed-bearing plants and spore-bearing plants. Seed-bearing plants include gymnosperms which produce naked seeds, and angiosperms which have seeds enclosed in ovaries. Angiosperms are divided into dicots and monocots. Plants can also be classified based on their life cycle as annuals, biennials, or perennials.