Mother Earth News has had interesting stuff about how roselle is good for lowering blood pressure --
http://www.motherearthnews.com/natur...#axzz34ZJXyGr4
A neat thing about roselle is that you don't have to just wait til late in the season to harvest the calyxes -- you can also harvest the leaves and make tea from them too, or use them in salads. (Dunno if the leaves also have the lowering blood pressure quality, but they taste good!)