The characteristic that is shared by both nonvascular and vascular plants and can therefore be placed in the overlapping section of the Venn diagram is:
2. perform photosynthesis
Both nonvascular and vascular plants carry out photosynthesis, although their structures and processes may differ. The other characteristics listed (having roots, having xylem and phloem, and producing seeds) are specific to vascular plants or do not apply to nonvascular plants.