Hi friends,
some things I found out & like to share when wondering about translucency on single sided leaves.
-Instead of using a Diffuse + greenish RGB Spectrum for transmission, you can also create something similiar looking by creating a Specular material:
Set its reflectance to "0", its index (refraction) to "1" and increase its roughness value.
Now plug your leaf texture to the transmission port, done.
This also looks good when used in a 50/50 mix with your old diffuse material.
even better: Use Photoshop to create some additional textures: bump, transmission, opacity.
Will boost realism a lot, even on low-res leaf geometry.
All test renders were lit by a huge emitter with a strength of 23.000 and no extra environment light.
pathtracing.