The plant world is conveniently separated into two major groups: the nonvascular plants and the vascular plants. The nonvascular plants include the bryophytes, while the vascular plants include the ferns, gymnosperms, and angiosperms. The nonvascular plants have no internal transport system. The vascular plants do have such a system, and they are more structurally and functionally complex.
Highly specialized tissues occur in the vascular plants. (A tissue is a group of cells working together to carry out a specialized function.) The tissues are organized into specialized organs called roots, stems, and leaves. The organs all contain the internal vascular system and are connected to one another by the system. The internal vascular system is composed of xylem and phloem.
Different combinations of tissues make up the organs of a vascular plant. In vascular plants, four types of tissues may be found: vascular tissue, ground tissue, dermal tissue, and meristematic tissue.