Yerba mate, what is it?

After feeling tired last night someone suggested that I have some Yerba Mate tea. Not knowing what it was I decided to try it. It's caffeinated but gave me a very fresh nice lift and helped me stay a little more alert until the early hours of the morning.

Apparently it gives you less of a come down than other energy products.

Yerba Mate is a species of holly from South America and is an ancient energy tea. Full info can be found on Wikipedia.