C. frutescens is a relatively uncultivated species. There is, of course, one tremendously famous variety, beloved of steak tatare and bloody mary fans; the tabasco. Tabascos, as used in the eponymous sauce, used to be grown entirely on Avery Island, Louisiana and even now that is the origin of all the seed stock used to produce peppers for the McIllhenny Company. The other reasonably well known frutescens variety is Piri Piri but the above flower is neither, it's on a bird type pepper known as Duke Pequin. For years people have pondered whether C. frutescens is an actual species or just a form of C. chinense.
Above is a C. chinense flower (variety is PI248129 (it doesn't have a name - just an accession number). You can see they are very similar. The chinense varieties are more well known and there are many more of them; scotch bonnets, habaneros and so on as well as the superhot forms like the trinidad scorpion (of which the Butch T strain is now the hottest chilli in the world) and seven pot. Where things get really interesting is with the famous superhot Bhut Jolokhia which is, it turns out, an interspecific hybrid somewhere between frutescens and chinense. Recent studies show that in fact, no matter which species concept you adhere to, frutescens is its own species and sits somewhere between C. chinense and C. annum (though far closer to C. chinense).
Here's an annum variety. As you can see it looks different to the other two. If you try to imagine something sitting between it and chinense though? I think you get something looking rather like that top photo.