This is an interesting case. We have Erica x darleyensis listed in our database, but we probably shouldn't. According to the Catalogue of Life, no such name exists. The Plant List calls it an unresolved name, which usually means it doesn't exist.
The "x" before a species name denotes a hybrid taxon -- a natural hybrid of two species. Sometimes these names disappear because the two species turn out to be the same plant. I remember when many plants were sold as Spiraea x bumalda, for instance. It was supposed to be a cross between Spiraea albiflora and Spiraea japonica. Then S. albiflora was discovered to be a mere synonym of S. japonica, so the hybrid taxon no longer existed because it was a cross between S. japonica and S. japonica -- in other words, not a cross at all.
I just did some digging and found that this is exactly what happened to Erica x darleyensis. It was supposed to be a natural hybrid of E. carnea and E. erigena. I see that Erica erigena is now a synonym for Erica carnea subsp. occidentalis, so I'll have to clean up our database accordingly and change a lot of entries tomorrow. I've added Erica carnea 'Eva Gold' for you.
Darley Dale Heath (Erica 'Eva Gold')
Sorry to talk your ear off in this post, but I found this interesting.
