This is a realy good site if you don't know what they look like but it is only a limited list there really are sooo..... many as I am finding out
http://www.tlady.clara.net/TortGuide/Diet.htm#plantlist
There is also some good pictures and a list under
http://shelledwarriors.co.uk/ Edible weeds
You could always grow you own they sell seeds in the SW shop......
Hope this helps