Hi
The plant finder should be giving the correct name and we should always go by this.
Orinally the plant was listed as microphylla I assume that the RHS have reviewed since then.
It is a plant that we had as a new introduction last year but not exclusive.
Quite often the first flowers will open either pure white or pure red, but they will change to the red lipped flowers which is how it got its name.
It originated from San Francisco Botanical Garden, having been found by Richard Turner - editor of Pacific Hort Magazine, his Mexican Maid had included it a floral disply, plants which had originated in Mexico.
I have a picture somewhere.
I also have the plant in my garden, it overwinters well, keeping its leave all winter. Needs a sheltered well drained spot, ideally quite dry in the winter. Other than a light prune its quite trouble free.