Tweetytunes: You are right about needing to break up the plants with a bit of color, they are paint effects plants, but as mentalray won't render them I've had to convert them to polys and then duplicate into instances, which is a pain, but I'm going to see wether I can add a bit of color to them as they are with some other shaders, not sure if it'll work but here's hoping!

Just checked out that cmd line render tutorial, learnt how to use the command line render really easily, Tweetytunes is right, such a good link, everyone should check that one out, thanks so much Chirone!