When you use 4.7, try to enable “two sided foilage” as the shading mode + connect the diffuse with subsurface -> that will probably solve the problem with the black parts 
e.g then you can reach such an effect as you can see here in this thread: https://forums.unrealengine/showthread.php?32543-What-Are-You-Working-On-Community-Screenshots-amp-Videos/page7 (the tree -> was made with the new shading mode)