Hi Chillybean,
To add a common name, find the plant in the database ... for instance
Deflexed Bottle-Brush Sedge (Carex retrorsa) 
Scroll down to where it says: Editing Actions
Click on: Edit Plant Name
Next to where it says Common Name you will see a tiny green + sign. Click there and type a common name into the empty box then scroll to the bottom and click on the green area that says Submit Your Proposed Changes.
