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).
These slides show the internal organization of monocot and dicot leaves. The epidermis produces a surface waterproofing substance called the waxy_cuticle. The upper and lower epidermis have specialized guard_cells that open and close, thereby creating air/water transfer spaces called stomata (stoma). In some texts, the guard cells plus the opening they create (called a pore, stoma, or stomate) are referred to collectively as a stomate.
In a monocot leaf, the vascular_bundles of xylem and phloem are arranged in a row, like a string of beads. Some of the vascular bundles are surrounded by a special layer of parenchyma (sometimes collenchyma or sclerenchyma) cells called the bundle_sheath_cells. These cells provide support and protection for the veins of vascular tissue, which are clearly visible on the leaf's surface.
The monocot micrograph also labels some surface cells as bulliform_cells. These bulliform cells are often used as "collapsable" cells that cause the leaf to fold shut, thereby preventing water loss. The bulbil_cells in this particular micrograph are used for vegetative_propagation.
The dicot leaf section shows the "dicot placement pattern" of vascular_bundles and stomata in the epidermal layer.