So the climbing plant is just about ready to go into UDK.

The Process

To create the textures I first created leaf and branch textures in Photoshop, I then applied them to the mesh in Zbrush. The leaves each had an individual UV map from earlier before I duplicated them everywhere - so I knew that the leaf texture would work. The tree branches' UVs were created in Zbrush and then I imported a texture from Photoshop. 

One important step is to add some colour variation to your leaves otherwise they'll just all be one colour and it will look like a block of green. I did this by polypainting in Zbrush. You need to first polypaint from texture (using your leaf texture). Then using the paintbrush with colourise turned on and RGB (turn off Zadd/sub) you can paint over the current texture. I turned the brush strength right down to just 1 and then painted different shades over the leaves. I just used a yellow randomly applying it to various leaves and that seemed to work quite well. You are basically painting on the vertex - so if your mesh doesn't have enough divisions this could be an issue (just sub-divide more). You can do something similar in UDK but it would have taken far too long with all those leaves.

Finally I used the GoZ funtion to extract both the normal map and diffuse map. I created specular and gloss maps in Photoshop.

The image on the left is the plant tiling x3 to give me some idea how it will look as a whole. The Ivy is on a plane of 18 polys - so very low. The 3D appearance is mainly created from the normal map (below). It's using an alpha channel at the moment for transparency.