I’ve cleaned up the code and posted source for my Processing L-system trees:

http://www.blprnt.com/processing/cherrytree/
http://www.blprnt.com/processing/birchtree/
http://www.blprnt.com/processing/showtree/

All three are quite similar. The birch and the cherry have slightly different leaves and slightly different tree-rendering settings - they also gather their colours from different images. The show tree is my webcam tree, and requires a webcam to be connected.

Some easy fun could be had with these by editing the Leaf class - it’d be cool to see what people come up with.