Lactuca Virosa is the latin name for wild lettuce. Though in some cases Lactuca serriola is also referred to as wild lettuce. Both have the sap with analgesic properties (technically common lettuce, Lactuca sativa, does as well).
It's not very tasty, hence it's other common name "bitter lettuce" but it makes a reasonably relaxing smoke. I don't believe I've put it in a changa blend, if I have it was with a bunch of other relaxing herbs, so I can't really say how it effects the experience on it's own. It's certainly something that you could experiment with.