When you place a group of plants you have a choice to turn on Mass Planting. If you activate the mass planting option, Vectorworks will group your plants together removing all of the lines with the plants overlap. In the image you can see two groups of identical plants. The left group of plants has Mass Planting activated, the group of plants on the right has Mass Planting deactivated. You can see the difference between the two groups of plants – one just shows a large shape, the other shows individual plants and it shows them overlapping.