http://en.wikipedia.org/wiki/L-system
http://algorithmicbotany.org/papers/abop/abop-ch1.pdf
https://graphics.ethz.ch/Downloads/Publications/Papers/2001/p_Par01.pdf
http://www.citygen.net/files/citygen_gdtw07.pdf
For later follow up. I've got some other things to check offline as well. I'll put up a more thorough post when I've had chance to look through them some more.