Bryophytes are three phyla of nonvascular plants, comprised of around 16,000 species including the mosses, liverworts, and hornworts. Called nonvascular, bryophytes lack a developed vascular system for the internal conduction of water and nutrients. It typically takes two generations to complete a plants life cycle, this is called alternation of generations, the regular alternation of a sexual with an asexual generation. Because they lack a vascular system and since the gametes require water for dispersal, bryophytes are generally small plants found in moist conditions, although, some have adapted to desert life. The other phyla, tracheophytes, are called vascular plants.
Vascular plants carry water and nutrients up and down the plant.
The two types of vascular tissue are xylem, which conducts water and minerals from the ground to stems and leaves, and the phloem, which conducts food produced by photosynthesis in the leaves to the stems, roots, and for storage and reproductive organs. The presence of vascular tissue is not the only differentiating feature the tracheophytes possess. This evolution, combined with the vascular nature of these plants has allowed the tracheophytes to dominate all terrestrial habitats of the Earth, save higher Arctic regions, and they also provide food and shelter for animal life on Earth. The Study of Plants All of the more than 260,000 species of plants differ from one another in one or more, sometimes minute, ways. Just as they differ, plants also have many common features.