Jamaica (Hibiscus) flowers - found dried in ethnic/Hispanic stores - have apparently proven to lower blood pressure.
http://www.webmd.com/heart/news/20081110/hibiscus-tea-may-cut-blood-pressure
Hibiscus tea is considered to be helpful for lowering cholesterol when drunk freely, and also helps the urinary system. It is cooling, I make it in the summer. Goes well with fruit juice. I use it in the winter in herb blends.