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.
The Angiosperms (flowering plants) are divided into two design categories, based in part upon the placement of their vascular tissues. The two categories are monocotyledons (monocots) and dicotyledons (dicots).
Monocot and dicot roots have the same overall organization because they do the same jobs, including water absorption. The outer layer of root tissue is the epidermis, the storage layer is called the cortex and an inner circular arrangement of cells called the endodermal_ring (with Casparian_strip) surrounds the centrally located vascular tissues.
The endodermal ring creates a one-way flow route for water with dissolved minerals. Once water is moved by passive transport through the epidermis and the cortex, it must cross the endodermal ring. The Casparian strip with waterproofing suberin prevents the water from going back out into the cortex. Therefore, the water is forced to move up the xylem tubes into the stem and leaves of the plant.
So, if the monocot root and the dicot root both have centrally located vascular tissues surrounded by an endodermal layer, how do we distinguish between the two? Easy - the arrangement of the vascular tissues of a monocot differs from that of the dicot. The monocot root has a ring or a random placement of vascular tissues. The dicot root has a pointy or star-shaped arrangement of vascular tissues.