Every summer when I go to AfroFest here, I head straight for one of the Caribbean food stands that serves the sorrel drink. It's made from the flowers of the plant and is just so tasty and refreshing.
Now the problem is, due to the discussions above, I googled sorrel and there are quite a few plants with that name, and I don't know which they use. The drink is purplish though and a bit astringent, but very flavourful and a real thirst quencher on a hot day.
Guess we'll have to get down to the Latin names here, but if anyone knows just which is used to make the drink, I'd love to know.