If you are just typing a generic name like begonia or coleus because you may not know the cultivar and there isn't an existing parent plant/custom database entry for it, it can't link up. We have a generic coleus page
Coleus (Coleus scutellarioides) but not one for begonia yet.
Typos are the best reason to link them from the database entry!
And if you have an inventory list of your plants, it should be easy to find the entry you need for tagging.