Most plants, if not terribly rare, will be easily identifiable from the shape and layout of the leaves under submerged growth, so should be relatively easy to I'd if you let them grow and you are sure the leaves of their underwater form. I was saying to grow some emerged if necessary, it looks to already be growing submerged.
Most plants will not flower underwater, so if the plant cannot be identified just visually from the leaves, it may be required to grow them emersed, and identify from the flower using scientific methods, botanists and that sort of thing.
Normally if you collect plants from the wild, or steal from someone else's tank, you may need identification assistance, if you buy from a reputable LFS, they normally know what they are selling.
We have grabbed random unmarked lilies from a tub outside of a saltwater aquarium store (we were allowed to)... We had no idea what it was, until yesterday Dr. Ted Coletti identified it as Nymphaea "Attraction"
I know your aversion to fish clubs, or I would suggest you go listen to Amanda Wenger talk about plant propagation and identification a week on Thursday