I have appreciated being able to make a comprehensive list of most/all of my plants but wonder if there is an option to enter pictures of plants that I don't have the specific cultivar name of? For instance, I have some begonias that I would like to record but I don't know the particular type or name. Thank-you.

You can use the "parent entry" for your unknown, and post your own photos in the comments section of your list. Here's the parent entry for begonias:
Begonias (Begonia)

There is also some talk of making changes that would allow more flexibility to the lists. You might be interested in this discussion:
The thread "Adding plants to your list if the plant doesn't exist in the database..." in Site Talk forum