Lynn,
My understanding is that either you accept Jovibarba as a genus and lump hirta and arenaria and the other rollers with heuffelii OR you accept them ALL as Sempervivum, including heuffelii. The second option was how Praegar named them and we will have to go back and changed Jovibarba hirta to Sempervivum hirtum so that the Latin names agree! We need Polly back to explain the rules of Latin. She had 6 years of it!
The Jovibarba genus is well resolved cladistically because of the floral morphology and chromosome counts. Also the Jovibarba species will cross with each other (although the offspring are close to sterile) but they cross with difficulty to Sempervivum and those are VERY sterile.
This is a classic lumpers vs. splitters controversy.
Hope that helps!
Kevin
