As you probably know, the four essential life elements are sun, air, water, and earth. So, the symbol at the top left is one of those four essential elements - the sun! In Plant Nanny², whenever you've fully raised three different kinds of plants in the greenhouse you can then use the sun to increase the greenhouse's level. As its level increases, its ability to produce seeds will increase. Additionally, once the greenhouse has reached its highest possible level you'll be able to attract a cute mystery creature to come join you in your greenhouse!