not sure whats happening here, what i did was make a tree with the sapling addon, converted the tree curve into a mesh, and then joined the leaves to the tree mesh.
The leaves show up in solid view (http://gyazo.com/0101563a7bea556b34f1e4d5c1e2a811) But not rendered view or rendered?
No blend file supplied with the post and not even a screenshot of the important info !!
Check outliner window incase you turned off renderability of the leaves
Check object / duplication to ensure you haven’t changed it from the default ‘None’ setting
Check render layers are correct
Maybe you turned on backface culling? Try turning it off and see if it works.
none of that helped, but i found a work-around, instead of going with the sapling addon leaves i’ve just made my own leaves. seems to be working now 