Ok I looked again. Really, I am so scatterbrained this week! The little leaved sedum is S. acre "Golden Carpet".
Yes the S. acre is the genus and species, but the name after is the "cultivar". Cultivar stands for "cultivated variety", sometimes if the plant is just a selection from nature, a geographically isolated type, a sport, or a mutation from a known Genus and species but is not widely cultivated it is just called a "variety". Sometimes you can have "forms", same Genus and species, but the plant appears slightly different. Sometimes these have been widely researched, sometimes not. Sometimes "forms" after more research fall into another species or new species. Sometimes they just have a different flower color or some minor deviation from the recognized species.
The sempervivums we most often discuss are Sempervivum tectorum "Cultivars" or Sempervivum arachnoideum "variety" or "Cultivar". Although to make this a bit more confusing there are I'm sure some interspecific crosses in the "Cultivars". For example: the plants I like with the "bloom" or glaucus look have been most likely interspecificly crossed (S. tectorum x S. calcareum) in their background at some point to move in the glaucus look. Cultivars which have the cilia or "hairs" are most likely products of having moved the cross S. tectorum x S. arachnoideum into their background at some point. Cultivars that are diminuative are most likely products of having crossed S. tectorum x S. montanum at some point.
Wow I got waaaay off topic there!