Well; I've had pneumonia for the last week, and it's still going strong... So, I've had some time to play with some trees :)

Here is one after culling the poly count down to 52,000 or so. For anything closer than that (or larger) it would need more polys, I think.

---

I found that the exported trees aren't UVMapped. Mapping the leaves is simple, but unwrapping a curved trunk and all the branches is a pretty big job. The branches :cursing:
I've also been looking at using square leaves, and applying a image transmap for the shapes. The transmaps are derived from photographic leaf textures. A 1024x1024, made up of 16 (256x256) similar but not identical leaves with a corresponding transmap seems to give enough variety. The square leaf meshes (I've been using 2x2 planes for far shots, 3x3 or 4x4 for closer) can be twisted around into various shapes w/ mesh noise and/or displacement to add a bit more variety.
The poly counts for the transmapped leaves are much lower, and a photograhic leaf texture looks better, IMO, than any procedural shader.
The render times seem about the same, or slightly less, with the transmapped method, unless I go overboard with the leaf polys. I have to force 2-sided rendering on the leaves either way; but this way, I can force 2-sided on the leaves but not the trunk and branches, so that saves some time.

The main difficulty has been making it look other than 16 leaves copied over the surface. Adding some procedural variation to the image texture and mesh shape has helped.

Friends don't let friends use booleans.