An attachable or built-in planter for your car for small plants, flowers, or cactuses. Could be up on the dash or in the middle panel or back seat area. The lip is designed so that water and dirt don't go everywhere when you stop/turn quickly. A watering portal and overwater tray allow you to manage the plant without making a mess.
It thrives in the natural heat/humidity of your car and makes you feel like your car is not ruining the Earth even when it is.-- napoleonbag, May 13 2008random, halfbakery