So I spun another quick idea or two whilst listening to the news. One involves spiders, t'other involves the orbits of moons around planets. I'm going with the plant idea.
Turns out that Unity3d have disabled shadows in the Indie (eg: cheap) version of the engine. Slightly narked about it but it's only a bloody shadow and it's only a bloody prototype, innit.
Also, I need an artist. My modelling skills are lacklustre. You can tell I've not done it for a decade.