Roots, Stems and Leaves
Plants are placed into two simple kingdom subsections: nonvascular and vascular plants. The big distinction between the two groups is that vascular plants have vascular tissues: tissues that conduct water and dissolved food in the plant body. The vascular tissues include xylem, which moves water and minerals upward through the plant and phloem, which moves dissolved food downward in the plant.
Nonvascular plants lack these tubes, and therefore must be small and thin so that each cell can acquire its needed materials via passive transport from the plant's surface, or from other cells within the plant that are located near the surface.
Regardless of whether a plant is vascular or nonvascular, it has structures that (1) anchor it into the soil, (2) provide physical support for its photosynthetic structures, and (3) specialize in performing photosynthesis.
The difference is that in nonvascular plants these structures are called root-like, stem-like, and leaf-like because they lack vascular tissues. True roots, stems, and leaves are those body structures that contain vascular tissues.
In the Angiosperm classification group (flowering plants), we classify the members of the group into two categories (monocots or dicots) based in part upon the physical arrangement of the vascular tissues in their roots, stems, and leaves.