Psilotum longitudinal section of sporangia within the synangium
Psilotum cross-section of sporangia within the synangium
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.
Psilotum is a primitive seedless vascular plant and is unique among vascular plants because it has no true roots or leaves. Its just a simple shoot system. Photo Atlas micrographs 47A and 47B show the shoot, which is called the prophyll. The synangium is a compound sorus (a sorus is a cluster of sporangia).
This graphic is reprinted with the permission of Thomson Learning/Brooks Cole Publishers, publishers of our laboratory Photo Atlas (Perry and Morton).