In all nonvascular plants, the gametophyte generation is dominant. Sporophytes grow from these gametophytes and need them as they provide them with the nutrients and water they need to survive. Non-vascular plants lack xylem and phloem which are part of the conducting tissue in higher plants. These tissues transport food and oxygen throughout a vascular plant. These are among the simplest of plants with no roots, stems, or leaves, just a thallus. They also don't possess flowers, a sexual reproductive organ found in higher plants. However, thallophytes are usually multicellular organisms as seen in mosses and liverworts, for example.