It wasn't in the database, not sure why you were unable to add it, usually it's because the fields were not filled in correctly. It should look like this:
Common name: Azalea
Genus: Rhododendron
Cultivar: Southern Charm
I created the entry for you here:
Azalea (Rhododendron 'Southern Charm')
Another way to search for entries is open the rhododendron database and search alphabetically.
